A significant winter storm signal has emerged for January 24-25 amid an ongoing Arctic pattern. Confidence is high for the first three days showing cold, dry conditions, but low to moderate for the weekend precipitation event where model spread exceeds 30°F on high temperatures. The NWS Sterling office explicitly increased their winter storm potential assessment on January 19, 2026, though exact track, intensity, and precipitation type remain highly uncertain at this range. Temperatures will run 10-25°F below normal through the period, with the coldest conditions Sunday into early next week following any storm passage.
A strongly negative Arctic Oscillation (-AO) is driving successive Arctic high pressure systems into the central and eastern United States. This pattern promotes sustained cold air masses and creates favorable upper-level dynamics for potential coastal cyclogenesis. The synoptic setup shows a deep upper trough over the eastern U.S. with multiple shortwave disturbances rotating through the base of the trough.
Three distinct phases characterize this forecast period:
Phase 1 (Jan 20-21): Post-frontal Arctic high pressure with the coldest morning of the period (lows 13-19°F). Strong pressure gradient produces breezy northwest winds. Temperatures struggle to reach 30°F Tuesday.
Phase 2 (Jan 22-23): Brief southwest flow ahead of approaching cold front allows temperatures to recover toward seasonal norms (highs near 50°F Thursday). Cold front passage late Thursday ushers in sharply colder air.
Phase 3 (Jan 24-26): Reinforcing Arctic front late Friday. Upper-level energy moving through the base of the trough may interact with Gulf moisture and coastal baroclinic zone. Pattern is favorable for significant winter storm development, though track determines impacts. Deep cold air entrenches by Sunday with highs potentially failing to reach 25°F.
| Date | High °F (P10/P50/P90) | Low °F (P10/P50/P90) | PoP | Precip (P50/P90) | Wind mph | Sky | Confidence |
|---|---|---|---|---|---|---|---|
| Tue 1/20 | 27 / 30 / 33 | 13 / 17 / 20 | 0% | 0.00" / 0.00" | WNW 12-18, G25 | Sunny | High (90%) |
| Wed 1/21 | 39 / 42 / 45 | 14 / 17 / 21 | 0% | 0.00" / 0.00" | S 8-14 | Sunny | High (85%) |
| Thu 1/22 | 48 / 51 / 54 | 28 / 32 / 35 | 5% | 0.00" / 0.00" | SSW 8-16, G25 | Ptly Cloudy | High (80%) |
| Fri 1/23 | 34 / 39 / 44 | 14 / 19 / 24 | 15% | 0.00" / Trace | NW 12-20, G28 | Cloudy | Medium (65%) |
| Sat 1/24 | 18 / 26 / 38 | 10 / 14 / 18 | 45% | 0.20" / 1.00" | NE-N 8-15 | Overcast | Low (35%) |
| Sun 1/25 | 20 / 26 / 34 | 8 / 14 / 18 | 40% | 0.10" / 0.50" | NW 10-18 | M. Cloudy | Low (40%) |
| Mon 1/26 | 24 / 32 / 42 | 6 / 12 / 18 | 5% | 0.00" / Trace | NW 6-12 | Clearing | Medium (55%) |
Probability interpretation: P10 represents the 10th percentile (colder/lower outcome), P50 is the median expectation, P90 represents the 90th percentile (warmer/higher outcome). Wide spreads indicate high uncertainty.
Expect a bitterly cold but sunny day with high pressure in control. The high temperature has a 90% probability of remaining between 27-33°F, with the most likely value near 30°F. Morning temperatures will be the coldest of the period, starting in the mid-to-upper teens. Northwest winds of 12-18 mph will produce wind chills in the single digits to low teens during the morning, improving to the teens by afternoon. There is zero precipitation risk. Conditions favor frostbite on exposed skin within 30 minutes during morning hours.
Moderation begins as winds shift southerly and Arctic high slides east. High temperatures climb to the low 40s with 85% confidence in the 39-45°F range. Morning lows remain cold (14-21°F) before southerly flow takes over. Skies remain sunny with increasing high clouds by evening. This will be the most pleasant day of the forecast period. No precipitation expected.
The warmest day of the week with highs approaching 50°F (P50 = 51°F). Strong agreement across models places this day's high between 48-54°F with 80% confidence. Southwest winds of 8-16 mph with gusts to 25 mph possible by afternoon ahead of approaching cold front. Clouds increase through the day. A 5% precipitation chance exists, primarily for areas south of Herndon near the I-64 corridor. The cold front passage is expected late evening to overnight.
Transition day with increasing uncertainty. High temperatures likely occur in the morning before falling through the afternoon as cold air floods in behind the front. Confidence drops to 65% with a spread of 34-44°F. The reinforcing Arctic front arrives late Friday into Saturday morning. Light precipitation (15% chance) is possible, primarily in the form of flurries or light snow showers, with accumulations unlikely. Northwest winds become gusty (12-20 mph, gusts to 28 mph) during the afternoon and evening.
This is the lowest confidence day with only 35% confidence in the specific forecast. Model spread is extraordinary: high temperatures range from 18°F (AccuWeather) to 54°F (LocalConditions), a 36°F divergence. The primary uncertainty involves timing of the potential coastal low development, its track relative to the coast, and the resulting precipitation type and intensity.
The median scenario (P50) suggests highs near 26°F with a 45% probability of measurable precipitation beginning as snow during the afternoon or evening hours. If precipitation occurs, the median expectation is approximately 0.20 inches liquid equivalent (2-4 inches snow at 10:1 ratio), but the P90 outcome could deliver 1.0 inch liquid equivalent (8-15 inches snow) if the storm tracks favorably.
Uncertainty remains elevated (40% confidence) though slightly improved from Saturday. The median forecast shows highs near 26°F with a 40% precipitation probability as any ongoing snow tapers and moves offshore. Cold air dominates regardless of storm track. If the storm materializes as a significant event, accumulating snow may continue into early Sunday before tapering. Arctic air locks in with lows potentially reaching single digits in outlying areas.
Confidence improves to 55% as the system exits and high pressure builds. Any lingering clouds clear through the day. Temperatures depend heavily on weekend snowpack and cloud evolution: the P10-P90 range spans 24-42°F for highs. Morning lows will be the coldest of the period if skies clear and snow cover is present, potentially dropping to single digits (P10 = 6°F). Dry conditions expected with clearing skies.
| Outcome | Probability | Description |
|---|---|---|
| No significant precipitation | 25% | Storm tracks too far offshore (>200 mi); brief flurries only |
| Light snow event (1-3") | 35% | Storm tracks offshore but close enough for light accumulations |
| Moderate snow event (4-8") | 25% | Storm tracks ~100 mi offshore; sustained snow with moderate totals |
| Major snow event (>8") | 15% | Near-benchmark track ~50-75 mi offshore; heavy snow possible |
If precipitation occurs, the most likely timing scenarios are:
Given the strong cold air mass in place, precipitation type discrimination favors snow over rain for this event.
| Type | Probability | Conditions |
|---|---|---|
| All snow | 60% | Surface temps below 32°F throughout event; deep cold column |
| Snow changing to sleet/ice pellets | 15% | Warm nose develops aloft; surface remains cold |
| Snow to freezing rain to rain | 10% | Storm tracks too close; warm sector briefly affects region |
| Primarily rain/mix | 15% | Storm tracks well inland; warm sector dominates |
If temperatures remain in the 15-25°F range during precipitation (most likely scenario), snow ratios of 12:1 to 15:1 are expected, yielding fluffy, wind-susceptible snow. If temperatures hover near 28-32°F during onset, ratios may decrease to 8:1 to 10:1, producing denser snow with higher water content.
| Accumulation | Probability |
|---|---|
| Trace - 1 inch | 35% |
| 1 - 3 inches | 25% |
| 3 - 6 inches | 20% |
| 6 - 10 inches | 12% |
| >10 inches | 8% |
1. Coastal low track and intensity The single largest source of forecast uncertainty is whether a coastal low pressure system develops and, if so, its precise track relative to the Mid-Atlantic coast. A track 50-75 miles offshore would maximize snowfall for the I-95 corridor. A track 150+ miles offshore limits impacts to light snow or flurries. A track that moves inland would bring warmer air and reduce snow totals or produce a rain/snow mix.
2. Cold air supply and CAD persistence Models historically show a warm bias during Cold Air Damming (CAD) events in the Virginia Piedmont. GFS specifically produces warm bias along the eastern Appalachians during CAD, meaning models may be too aggressive in eroding the cold air dome. If cold air persists longer than modeled, snow totals could overperform and precipitation type could remain colder than currently forecast.
3. Phasing of shortwave energy Multiple pieces of upper-level energy are rotating through the base of the trough. Whether these pieces phase (combine) into a single, stronger system or remain separate, weaker disturbances dramatically affects precipitation intensity and duration.
Scenario A: Offshore track (Probability: 30%) Storm develops but tracks more than 150 miles offshore. Result: Brief period of light snow or flurries Saturday night, accumulations under 2 inches. Sunday clearing. Temperatures as forecast.
Scenario B: Benchmark track (Probability: 25%) Storm develops and tracks 50-100 miles offshore. Result: Significant snowfall of 4-8+ inches Saturday night through Sunday morning. Travel impacts likely. Temperatures 2-5°F colder than P50 due to snowpack and clouds.
Scenario C: Inside track (Probability: 15%) Storm tracks over or just west of the region. Result: Precipitation begins as snow but changes to sleet, freezing rain, or rain during peak intensity. Mixed accumulations with potential ice accumulation of 0.1-0.25 inches. This scenario carries highest hazard risk.
Scenario D: System fails to organize (Probability: 30%) Upper-level energy remains disorganized; no significant coastal low develops. Result: Scattered snow showers with trace to 1 inch accumulations. Very cold temperatures dominate the story.
Given the characteristics of this event (winter storm potential, CAD environment, 5+ day lead time for key event), the following model weighting was applied:
| Model/System | Weight | Rationale |
|---|---|---|
| ECMWF IFS | 25% | Highest global skill; ~1 day accuracy advantage; 9 km resolution; strong winter storm performance |
| ECMWF ENS | 20% | 51-member ensemble provides probability distribution; superior to GEFS for medium-range uncertainty |
| NBM (National Blend) | 20% | Integrates 31+ model systems with bias correction; calibrated probabilities; best for consensus |
| GFS | 10% | Discounted due to known warm bias during CAD events; 16-day range useful for pattern confirmation |
| GEFS | 10% | 31 members provide uncertainty bounds; complements ECMWF ENS |
| HRRR | 5% | Only useful for Days 1-2; highest resolution for short-range timing |
| NAM | 5% | Wet bias requires adjustment; useful second opinion for CAD scenarios |
| AI Models (AIFS, GraphCast) | 5% | Strong for synoptic patterns; weak for precipitation; supplementary use only |
Why ECMWF is weighted most heavily: ECMWF maintains approximately one full day of forecast skill advantage over GFS in 500 hPa anomaly correlation. The June 2023 upgrade (Cycle 48r1) increased ENS resolution to 9 km, matching HRES. The November 2024 upgrade (Cycle 49r1) specifically improved 2-meter temperature forecasts through data assimilation improvements. For coastal winter storms affecting the Mid-Atlantic, ECMWF has historically shown superior track prediction.
Why GFS is discounted: Virginia Tech research (2007-2016) documented persistent warm bias on the east side of the Appalachians during CAD events. GFS and NAM both tend to erode cold air domes prematurely, leading to temperature forecast errors exceeding 8°F in bust cases. This bias is directly relevant to the January 24-25 event where CAD will influence precipitation type.
Why AI models receive minimal weight: While ECMWF AIFS became fully operational February 2025 and shows 20% improvement in tropical cyclone tracks, AI models systematically underpredict precipitation and struggle with record-breaking temperature extremes. GraphCast and Pangu-Weather explicitly exclude precipitation from their primary outputs due to ERA5 training data biases. For a winter storm event where precipitation type and amount are the key forecast challenges, physics-based NWP remains superior.
Ensemble interpretation methodology: P10/P50/P90 values were derived from the combined ensemble distribution (GEFS + ECMWF ENS weighted equally), adjusted for known model biases using NBM calibration curves. Weekend values carry asymmetric uncertainty skewed toward colder temperatures due to historical CAD warm bias in models.
| Metric | ECMWF | GFS | GEFS | Notes |
|---|---|---|---|---|
| 500 hPa ACC > 0.8 | ~10 days | ~9 days | - | ECMWF leads |
| 2m Temp MAE (Day 3) | ~2.0°F | ~2.5°F | - | ECMWF advantage |
| Winter storm track error | 75 mi | 100 mi | - | ECMWF more accurate |
| Precip timing | Good | Moderate | Spread captures | NBM calibrated |
Daily confidence scores incorporate:
Days 1-3 score High (80-90%) due to high pressure dominance and strong model agreement. Days 4-5 score Medium to Low (35-65%) due to storm system uncertainty and large model spread. Days 6-7 score Medium (55%) as post-storm conditions become more predictable.
This forecast is valid as of January 20, 2026, 00Z initialization. Given the high uncertainty associated with the January 24-25 potential winter storm, the following update schedule is recommended:
Monitor NWS Sterling (weather.gov/lwx) for official watches and warnings. Winter Storm Watch issuance is possible by Wednesday evening if models converge on a significant snow solution.