266
FOUS11 KWBC 261820
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT MON OCT 26 2026
VALID 00Z TUE OCT 27 2026 - 00Z FRI OCT 30 2026
..DAKOTAS INTO NORTHERN MINNESOTA
DAY 1...
A COMPACT SHORTWAVE AND WEAK SURFACE LOW WILL CONTINUE TO PRODUCE
DYNAMICALLY FORCED PRECIPITATION FROM PORTIONS OF NORTH-CENTRAL SD
AND SOUTH-CENTRAL ND INTO NORTHERN MN TONIGHT INTO TUESDAY MORNING.
DESPITE MARGINAL SURFACE TEMPERATURES, ENOUGH DYNAMIC COOLING WILL
BE PRESENT DIRECTLY UNDERNEATH THE POTENT SHORTWAVE ALOFT TO
SUPPORT PERIODS OF MAINLY LIGHT TO BRIEFLY MODERATE SNOW. ANY
ACCUMULATIONS OF A COATING UP TO AN INCH (OR TWO AT MOST) SHOULD
MAINLY BE CONFINED TO COLDER, ELEVATED, OR GRASSY SURFACES, WITH
LIMITED IMPACTS TO PAVED SURFACES. AS A RESULT, WSSI-P
PROBABILITIES FOR MINOR IMPACTS (WINTER DRIVING CONDITIONS OR A FEW
INCONVENIENCES TO DAILY LIFE) REMAIN LOW AT 20% OR LESS.
..CASCADES AND NORTHERN ROCKIES
DAYS 1-3...
AN ACTIVE AND UNSETTLED PATTERN IS ON TAP FOR THE NORTHWEST U.S.
THIS WEEK AS A SERIES OF LOW PRESSURE SYSTEMS AND SHORTWAVE TROUGHS
DIG SOUTHWARD ALONG THE BRITISH COLUMBIA COAST AND TRACK OVER THE
PACIFIC NORTHWEST. SNOW LEVELS ACROSS THE CASCADES WILL
PROGRESSIVELY LOWER WITH TIME, STARTING AROUND 5000FT TONIGHT,
DROPPING TO AROUND 4000FT TUESDAY NIGHT, THEN LOWERING TO AROUND
3000FT WEDNESDAY NIGHT INTO THURSDAY. SNOW IN THE CASCADES WILL
INITIALLY BE SHOWERY AND INTERMITTENT WITH MOSTLY LIGHT TO MODERATE
INTENSITY OUTSIDE OF HEAVIER BURSTS. HOWEVER, SNOW SHOULD BECOME
STEADIER AND HEAVIER TUESDAY NIGHT INTO WEDNESDAY BEFORE TURNING
SHOWERY AGAIN WEDNESDAY NIGHT INTO THURSDAY. THE PROBABILISTIC
PRECIPITATION PORTAL (PPP) SHOWS HIGH PROBABILITIES (>70%) FOR
ACCUMULATIONS >8" THROUGH THURSDAY, AND >50% PROBABILITIES FOR
>12", GREATEST IN THE HIGHER ELEVATIONS OF THE WASHINGTON CASCADES.
THE WSSI-P SHOWS 40-60% PROBABILITIES FOR MINOR IMPACTS AND WINTER
DRIVING CONDITIONS DOWN TO SNOQUALMIE AND STEVENS PASSES.
MEANWHILE, PERIODS OF MOUNTAIN SNOW WILL CONTINUE OVER THE
NORTHERN ROCKIES THROUGH THURSDAY WITH SNOW LEVELS FALLING AND THEN
GENERALLY HOVERING BETWEEN 4000FT AND 6000FT (LOWEST NORTH,
HIGHEST SOUTH). PRECIPITATION WILL INITIALLY BE FOCUSED ACROSS THE
HIGH ELEVATIONS OF EASTERN ID, NORTHWEST WY, AND SOUTHWEST MT
BEFORE SHIFTING NORTHWARD TO THE NORTHERN ID AND NORTHWEST MT
RANGES (INCLUDING THE LEWIS RANGE AND GLACIER NATIONAL PARK) BY
WEDNESDAY. INCREASING LARGE SCALE FORCING FOR ASCENT DOWNSTREAM OF
THE DISTURBANCES PIVOTING ACROSS THE PACIFIC NORTHWEST COMBINED
WITH INCREASING LOW-LEVEL NORTHEASTERLY/EASTERLY UPSLOPE FLOW SOUTH
OF AN ENCROACHING SURFACE HIGH WILL RESULT IN SOME LENGTHIER
PERIODS OF SNOW WITH INTENSITY THAT COULD BECOME HEAVY AT TIMES.
THE PPP SHOWS >50% PROBABILITIES FOR ACCUMULATIONS >8" ACROSS THE
HIGH ELEVATIONS OF EASTERN ID, SOUTHWEST MT, AND NORTHWEST WY...
AND >50% FOR ACCUMULATIONS >12" IN THE HIGH ELEVATIONS OF NORTHERN
ID AND NORTHWEST MT. WHILE THE GREATEST SNOW ACCUMULATIONS WILL
LIKELY STAY ABOVE PASS LEVEL, THE LATEST WSSI-P STILL SHOWS ~20-40%
PROBABILITIES OF MINOR IMPACTS AND WINTER DRIVING CONDITIONS AT
VARIOUS PASSES IN ID AND MT.
THE PROBABILITY OF SIGNIFICANT ICE ACROSS THE CONUS IS LESS THAN
10 PERCENT.
MILLER
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