A roadside stop for suspected impaired driving rarely turns on a single fact. Juries listen for a story that makes sense across conditions, timing, and behavior. Prosecutors look for straight lines: odor, eyes, slurred speech, poor field tests, a number on a printout. The work of a DUI Defense Lawyer is to pull the lens back and show what the scene really looked like. Weather, road surface, traffic rhythms, vehicle quirks, and the officer’s vantage point all matter. Ignoring those details is how defensible cases get pled as if there were no defenses at all.
I have defended drivers in mountain snow at dawn, suburban rain right after a heat wave, and summer nights where roadwork detours turned familiar routes into obstacle courses. The techniques below come from that kind of ground truth. They reflect the intersection of Criminal Defense Law and practical driving, not just textbook Criminal Law. They also carry over to cases where DUI allegations overlap with assault allegations during an arrest, drug possession found after a stop, or even more serious accusations handled by a seasoned Criminal Defense Lawyer. Facts are the raw material. Conditions shape how those facts should be read.
The physics of impairment evidence
DUI evidence often hinges on human observation. What looks like impairment can be ordinary physics. A sedan hits standing water at 45 mph, the steering lightens, traction control pulses, and the car shimmies. To a following officer, that can read as weaving. A pickup with worn shocks on a grooved highway may “hunt” along the ruts. A driver cresting a hill into a crosswind might correct twice within a lane. Each of those maneuvers can appear on video as lateral movement and can be described in a report as “unable to maintain lane.”
The question in court is not whether movement occurred, but whether the movement proves impairment beyond a reasonable doubt. When weather and road conditions explain the same behavior, jurors have a safe alternative that aligns with common sense. A DUI Lawyer should investigate first, not argue from memory. That means an actual site visit when possible, or at minimum, documented condition checks through weather records, maintenance logs, and high-quality mapping.
Weather as an expert witness you did not call
Weather is both an explanation and an experimental control. If rain began at 9:12 pm and the stop occurred at 9:17 pm, the first few minutes of precipitation lift oil and brake dust to the surface and make the road slicker than a downpour an hour later. In my files, the most common weather-linked fact patterns include light rain after a dry spell, freezing fog at elevations over 1,500 feet, rapid temperature drops at dusk that cause bridge icing, and gusty crosswinds along river corridors. Each of these has a signature in driving patterns and field tests.
Light rain combined with oncoming headlights can make roadway markings harder to parse. Reflective paint blooms under wet glare. Drivers drift toward the center to avoid puddles near the shoulder. That is normal defensive driving, not an index of impairment. In one case, a patrol car video captured a suspect’s tires touching the inside of the fog line three times over half a mile. The officer cited that as “multiple lane departures.” The map and the post-stop walk confirmed that the fog line ran along a section with poor drainage and two collapsed shoulder points. The jury saw drivers ahead making the same correction.
Cold and wind play tricks on the horizontal gaze nystagmus test. The eyes track a stimulus, and the officer looks for involuntary jerking that correlates with alcohol. Yet cold air and bright strobe lights from a cruiser can induce tearing and squinting. In wind, the subject often turns their head slightly to steady the target, which breaks test protocol. I cross-examine on these micro-factors and, when justified, use an expert to walk through how they degrade reliability. Defensive driving in the rain can also change following distance and brake timing, which can look like “delayed response” if someone is eager to see delay.
A careful defense will collect:
- Archived hourly weather data, radar snapshots, and METAR reports from the nearest airport or weather station to pin down precipitation type, timing, visibility, wind speed, and temperature.
Road surface, maintenance history, and how cars really behave
A road is not just asphalt. It is a texture, slope, crown, camber, and a set of grooves created by heavy trucks. It is paint that may be old or freshly applied. It is a collection of temporary patches that create uneven elevation. A defense lawyer who has never walked the scene misses what the driver felt through the wheel.
Fresh micro-surface work can leave stone chips that roll under tires. A straight-line braking test on such a surface will print longer scuff marks and a slight pulsing from ABS, captured on video as “skidding” even with careful braking. Raised reflectors used as lane markers will kick a motorcycle over an inch if hit at the wrong angle. Converging lane lines near on-ramps, with rumble strips cut into the shoulder, prompt sudden corrections by cautious drivers who think they are about to drift off the roadway. All of this is visible during a daylight site visit and can be preserved with smartphone photos tagged by GPS and timestamp, or body cam review if the officer walked the area.
Notably, the National Highway Traffic Safety Administration’s validation studies for standardized field sobriety tests account for flat, dry, non-slippery surfaces. The studies do not claim accuracy on sloped or uneven ground, gravel shoulders, or in stiff wind. When the officer places a suspect on a crowned lane with minor aggregate rollover, clues like “stepped off line” or “swayed” lose diagnostic force. I often request the patrol log to identify the exact spot used for field testing and the video angle. If the test happens on a damp shoulder with visible grit, I will play the video slowly so jurors can see the tiny foot slides the officer called “loss of balance.”
Night optics, glare, and how video misleads
Dash cameras and body cameras help more than they hurt when conditions are central. They also lie in particular ways. A wide-angle lens exaggerates lateral movement. Headlight bloom on wet pavement hides lane markings. The microphone picks up engine idle and background radio but loses soft-spoken instructions. If the officer and the driver talk over one another near a passing truck, the transcript printed later may show only the officer’s words.
I make a point of viewing the raw file on a large screen and then again on a smaller tablet to see how jurors might experience it. I mark seconds where glare erases the fog line or where the officer’s flashlight hits the camera lens and masks the suspect’s eyes during a nystagmus test. From there, the cross-examination writes itself. Was the camera calibrated to reflect true distance? How often has the officer tested the dash cam tilt after speed bumps? Did they review the footage before writing that the driver “nearly struck the curb,” or is that an impression that the video does not quite show?
Low light also changes how the human eye reads speed and distance. In patchy fog, drivers often reduce speed and hug the center line to better see reflected signage, which tends to sit on the median side in divided highways. It looks like a preference to the left, and to a following unit it can appear as poor lane control. Here, snapshots of the route in similar conditions, taken on different nights, can be persuasive. Jurors drive at night. They understand that not all drift is reckless.
Driving patterns worth charting, not just describing
Reports frequently rely on adjectives: weaving, drifting, delayed, abrupt. The defense should be concrete. When the squad car video shows two tire touches across a dotted line over 0.8 miles, that is not weaving in any meaningful sense. When brake taps occur at the same three downhill intersections, that is grade management, not nervous riding of the brakes. A short map with times plotted at known distance markers, even drawn on plain paper, reframes the behavior into data. The officer may have his own data via GPS pings. Ask for it. If not produced, make note of the absence.
On multi-lane roads, lane choice itself tells a story. Many sober drivers choose the right lane in heavy rain to avoid high-speed splash from the median. During snow, the left lane may remain clearer if plows focus inside-out. Video may show a car moving from right to left, which an officer writes as “passing multiple vehicles in poor conditions.” But the pace may be modest and the move simply reflects where traction exists. Pull the plow logs if the stop happened during active snow service. A jury will respond to the logic of following the clean lane.
The human body in cold, wet, or wind
Field sobriety tests presume the subject is steady, warm, and on a suitable surface. In practice, the officer often conducts them in 38-degree drizzle on an uneven shoulder. That context matters.
Standing still in cold wind exaggerates normal sway. Hands in pockets are instinctive, yet officers often instruct subjects to keep arms at their sides. When you see a person sway with hands pinned, you are watching basic balance mechanisms deprived of their normal aids. In rain, breath condenses forward and can mix with faint alcohol odor from a single drink, creating a stronger smell near the mouth and mustache. After a long day, conjunctival redness can come from fatigue, contacts, or wind. None of these signs equal impairment, but they can prime an officer already convinced by a driving pattern.
The walk-and-turn and one-leg stand tests degrade quickly when shoes are wet, when the ground is gritty, and when trucks push air. I have asked more than one officer whether they would feel confident performing those tests in dress shoes under those conditions. A few have answered honestly: not very. Jurors remember that.
Breath tests and environmental confounders
Breath testing in harsh weather introduces small but real variables. Breath temperature can run cooler after standing outside, which affects breath alcohol concentration estimates, though modern devices attempt to correct for this. Residual mouth alcohol from cough syrup or mouthwash dissipates over time, but the waiting period before testing is not uniformly honored or documented. If the subject was coughing in cold air, burping, or had reflux triggered by stress, the possibility of mouth alcohol contamination increases.
Outside the roadside context, the breath testing room may be near a garage bay or a booking area with solvent fumes, hand sanitizer vapor, or cleaning chemicals. Good devices detect interferents, but not all logs reflect those alerts, and not all agencies preserve quarterly interference checks with care. A Criminal Defense Lawyer should request not only the subject’s test record and device maintenance logs, but also any contemporaneous tests performed on other subjects that day to see whether anomalies cluster.
When the state relies on a portable breath test from the roadside, the environmental critique strengthens. Those devices are screening tools, not evidentiary in many jurisdictions. Cold exposure, battery status, and calibration drifts matter. Look for gaps: Was the 15-minute observation truly uninterrupted, or did the officer step away to run a plate? Did the wind direction blow exhaust across the sampling area? Where was the patrol car idling?
Linking conditions to probable cause
The first legal question often is whether the officer had reasonable suspicion for the stop and probable cause for arrest. Conditions fit both inquiries. A single touch of the fog line with no other violations is not a traffic offense in many states. Even where the statute bars “failing to maintain a lane,” case law often requires movement that affects safety. If the drift coincided with a gust or puddle, and if dash video shows other cars making similar corrections, the suspicion looks less particularized.
On probable cause, stack the conditions against the cues. Slight sway in cold wind, minor missteps on gravel, watery eyes in drizzle, and odor in a small space after a single admitted drink add up to ambiguity, not certainty. The weight of a DUI defense is not to prove sobriety, but to show that the officer’s interpretation was not the only reasonable one. That is the heart of Criminal Defense.
Crafting the narrative: witness selection and sequence
The sequence of witnesses can either highlight or bury your weather and road themes. Start with the reason for driving. A nurse leaving a late shift, a contractor returning tools during an unexpected rain, a parent retrieving a sick child from a sleepover. Ordinary life frames ordinary caution. Then bring the conditions to life. A neighbor who lives along the route can testify about how the shoulder floods after a hard sprinkle. A city maintenance worker can explain the new slurry seal that leaves loose aggregate for several days. If the budget allows, an accident reconstructionist or human factors specialist can testify about perception in glare and motion in crosswind. Keep experts tight. Jurors prefer concrete demonstrations and short explanations.
Use the officer on cross to fill gaps. Where were they parked in relation to the oncoming traffic and street lights? What angle did they have to the subject vehicle on curves? Did they note puddling, debris, or cones from roadwork? How many similar corrections did they observe from other drivers that hour? Did they check the wind advisory that evening? If the officer did none of these, the jury will see the simplicity of their inference.
Timing, fatigue, and the rhythm of traffic
Many stops occur just after bar closing, but plenty happen at 5:30 am or 3 pm. Fatigue impairs balance and recall. Morning commuters move at a steadier pace than late-night traffic, and their lane discipline differs. When sleepiness and circadian low collide with long straight roads, micro-corrections are common. Highlight the rhythm. Was there a strong headwind at dawn? At midday in summer, heat shimmer makes distant lane lines waver. People squint, lean forward, and change following distance.
Time stamps from the video give you speed, spacing, and maneuver frequency. If the subject made one allegedly abrupt correction at mile marker 14.2 as a truck merged, then drove flawlessly for 0.9 miles before the stop, that pattern is very different from continuous poor control. Jurors appreciate patterns. They also appreciate that humans are not metronomes.
Medical and mechanical confounders that mimic impairment
Weather and roads interact with the person and the machine. A driver with benign positional vertigo in gusty conditions will sway more. Diabetics with low blood sugar show confusion and sweet breath that officers sometimes misinterpret. A knee injury flares in cold. If your client has any of these, present it plainly, without drama. Demonstrate how someone without those issues would struggle with the same tasks under the same conditions.
Mechanical issues matter. A vehicle with worn tie rods or a misaligned rear axle will drift and require constant correction. In rain, that can feel like hydroplaning even at moderate speeds. Pull the service records. If the stop occurred just after a tire change, the torque pattern may have been uneven. A rental car often comes with unfamiliar controls and lane-assist beeps that confuse drivers who have never heard them. The defense should not overpromise, but a short, credible explanation beats a generic denial.
How prosecutors try to neutralize condition-based defenses
Expect the state to say that lots of people drove that night and only your client drew attention. They will claim the officer has training to distinguish weather drift from impairment. They will note any admission of drinking and anchor the narrative to that. Prepare for the standard retorts and meet them head-on.
Training is not omniscience. Officers are taught to recognize patterns, but many do not test their assumptions against data. Their reports often recycle phrases, and some departments incentivize DUI arrests in ways that bias interpretation. Ask how many stops the officer made that shift, how many led to DUI arrests, and what portion of those involved similar conditions. When forced to specifics, the aura of certainty softens.
On the “only your client” point, be ready with video timestamps showing other cars correcting in the same areas, or with testimony from road workers about recurring water accumulation. If you cannot find comparative footage, explain why: the camera field of view, darkness, or position made other cars difficult to capture. Do not overreach. Jurors punish overreach more than they punish cautious concessions.
Practical steps for defense lawyers during the first week of a case
Think about evidence as perishable. Weather and road states change quickly. The sooner you preserve reality, the stronger your case.
- Visit the scene at a similar time and, if possible, in similar weather. Photograph lane markings, shoulders, reflective paint, drainage, and testing locations. Save video drives in both directions.
Those early hours are where a case shifts from a single narrative to a layered one. A Defense Lawyer who treats conditions as central will spot issues that otherwise go unnoticed.
Intersections with other charges
DUI stops often lead to add-on allegations: resisting or assault on an officer when someone stumbles and hands are put on them, or a small baggie found in a pocket leading to a drug charge. An assault defense lawyer approaches body positioning, commands, and arm control with the same attention to surface and weather. Wet cuffs bind. A step backward on gravel can look like pulling away. For a drug lawyer, the justification for the search may tie back to the validity of the stop. If the stop lacks reasonable suspicion, suppression becomes viable.
In rare cases, a traffic stop becomes a flashpoint for serious felonies, even homicides in vehicular contexts. A murder lawyer analyzing a crash with intoxication allegations will lean on reconstruction, friction coefficients, and roadway design. The habit of grounding arguments in physical conditions, honed in DUI work, translates directly.
Jury persuasion: show, do not just tell
Facts about wind speed and rainfall totals bore jurors unless tied to what the driver felt in their hands and feet. Bring a short section of rumble strip salvaged from a construction source or a small board with similar texture. Have an expert or even the officer acknowledge what it feels like under a shoe. Display a photo of the exact fog line with puddle reflection. Keep the exhibits humble and authentic. You are not trying to impress with gadgets, but to restore the ordinary physics that the state has flattened into a story about drunkenness.
Remember cadence. Let the jury breathe with the timeline. “At 9:14 pm, the first drops hit. At 9:16, the car passes the low shoulder near Birch. Watch the right edge. See the glare. At 9:17, brake lights up ahead. Here’s the correction. Now a full half mile of steady center. That is not impairment, that is weather.”
Ethical guardrails and professional judgment
Condition-based defenses are not an invitation to manufacture doubt. If your client was truly impaired, negotiate responsibly. The public expects Criminal Defense to be vigorous and honest. Weather and road facts should be pursued when they exist, not invented by selective memory. The best DUI Lawyer I know has walked away from cases that he could have muddied, because safety and credibility matter long term.
When you do lean into conditions, be specific. A vague “it was raining” invites easy dismissal. A concrete “0.12 inches fell in the first ten minutes, after nine days without precipitation” sounds like what it is, a real factor.
What clients should document after a stop
Clients often ask what they can do beyond hiring counsel. I give a short, doable plan:
- Write a timeline that night or the next morning while details are fresh. Include weather, route, stops, food, medication, and vehicle quirks.
Simple records beat memory six months later in a courtroom. They also help a Criminal Defense Lawyer evaluate whether to bring in an expert or rely on lay testimony.
When to bring in experts, and when not to
Experts cost money and can backfire if the science outpaces juror patience. Use them when you need to translate conditions into mechanisms, not to repeat what a lay witness could say better. A human factors specialist helps when dash camera optics are central. A pavement engineer helps when you have objective proof of surface conditions that contradict the officer’s descriptions. In many municipal courts, however, a thoughtful cross, murder lawyer a few photos, and a credible client do more than a stack of credentials.
Closing the gap between law and lived driving
DUI enforcement sits at the intersection of policy and the messy reality of driving in weather on imperfect roads. A good Criminal Defense Lawyer recognizes that the law does not drive the car. People do, in rain and wind, with fears and habits, on surfaces that change. Conditions do not excuse dangerous behavior, but they do explain ordinary behavior misread through the lens of suspicion.
Build your defense from the ground up. Touch the pavement. Smell the air. Time the light cycle. Chart the grade. Then let the story unfold where it belongs, in the physical world where your client actually drove. If you can reconnect jurors to that world, you give them permission to apply the standard the law requires and to separate impairment from the many other forces that move a car down a road.