Prognostic Meteorological Discussion
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664
FXUS21 KWNC 231931
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 23 2017

SYNOPSIS: AN AREA OF UPPER-LEVEL LOW PRESSURE IS FORECAST OVER THE WESTERN U.S.
DURING THE NEXT WEEK, WHILE A STRENGTHENING AREA OF UPPER-LEVEL HIGH PRESSURE
BECOMES CENTERED OVER THE FLORIDA PENINSULA. SURFACE LOW DEVELOPMENT IS
EXPECTED ACROSS THE CENTRAL GREAT PLAINS BY TUESDAY, FEB 28. THIS SURFACE LOW
AND ITS TRAILING FRONT ARE FORECAST TO ADVANCE ACROSS THE CENTRAL AND EASTERN
U.S. DURING MID-WEEK. A PATTERN CHANGE IS BECOMING MORE LIKELY DURING WEEK-2
WITH A BUILDING RIDGE OF HIGH PRESSURE NEAR THE WEST COAST AND A DEVELOPING
AREA OF UPPER-LEVEL LOW PRESSURE OVER THE EAST-CENTRAL U.S.

HAZARDS

HEAVY SNOW FOR THE SIERRA MOUNTAINS AND PARTS OF WESTERN NEVADA, SUN-MON, FEB
26-27.

HEAVY SNOW FOR THE HIGHER ELEVATIONS OF ARIZONA AND COLORADO, MON-TUE, FEB
27-28.

HIGH WINDS FOR PARTS OF THE SOUTHWESTERN U.S. AND CENTRAL/SOUTHERN HIGH PLAINS,
MON-TUE, FEB 27-28.

CRITICAL FIRE WEATHER CONDITIONS FOR PARTS OF THE SOUTHERN HIGH PLAINS, TUE,
FEB 28.

HEAVY SNOW FOR PARTS OF THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES, TUE-WED,
FEB 28-MAR 1.

HEAVY RAIN FOR PARTS OF THE OHIO AND TENNESSEE VALLEYS AND CENTRAL
APPALACHIANS, TUE-WED, FEB 28-MAR 1.

MUCH BELOW-NORMAL TEMPERATURES FOR THE EASTERN INTERIOR OF ALASKA, THU, MAR 2.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC
NORTHWEST, NORTHERN GREAT BASIN, AND NORTHERN ROCKIES, FRI-SAT, MAR 3-4.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE ALASKA PANHANDLE, MUCH
OF MAINLAND ALASKA, AND PARTS OF THE ALASKA PENINSULA, FRI-THU, MAR 3-9.

A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF SOUTHEASTERN
MAINLAND ALASKA AND THE ALASKA PANHANDLE, FRI-SUN, MAR 3-5.

FLOODING POSSIBLE ACROSS PORTIONS OF THE UPPER AND MIDDLE MISSISSIPPI VALLEY
AND ALONG THE RED RIVER OF THE NORTH.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF IDAHO AND OREGON.

SEVERE DROUGHT ACROSS PORTIONS OF SOUTHERN CALIFORNIA, SOUTHWESTERN ARIZONA,
GREAT PLAINS, ARKANSAS, TENNESSEE VALLEY, SOUTHERN APPALACHIANS, AND THE
NORTHEAST.

DETAILED SUMMARY

FOR SUNDAY FEBRUARY 26 - THURSDAY MARCH 02: SPREAD AMONG DETERMINISTIC MODEL
SOLUTIONS IS LARGE AT THIS TIME RANGE, REGARDING A SHORTWAVE TROUGH ENTERING
THE WESTERN U.S. THIS WEEKEND, ITS DOWNSTREAM SURFACE LOW DEVELOPMENT, AND
ASSOCIATED PRECIPITATION AMOUNTS. THE LATEST MODEL GUIDANCE REDUCED
PRECIPITATION AMOUNTS ACROSS CALIFORNIA EARLY IN THE PERIOD AS THE SHORTWAVE
TROUGH TAPS INTO SUBTROPICAL MOISTURE FOR A LIMITED TIME IF ANY. HOWEVER, DUE
TO RELATIVELY LOW SNOW LEVELS, A HEAVY SNOW HAZARD IS MAINTAINED FOR THE SIERRA
MOUNTAINS AND WESTERN NEVADA ON FEB 26 AND 27. AS THE MID-LEVEL TROUGH SHIFTS
INLAND, HEAVY SNOW (6 INCHES OR MORE PER 24 HOURS) IS EXPECTED ACROSS THE
HIGHER ELEVATIONS OF ARIZONA AND THE COLORADO ROCKIES ON FEB 27 AND 28. HIGH
WINDS (SPEEDS ABOVE 35 KNOTS) ARE ALSO FORECAST TO DEVELOP ACROSS THE
SOUTHWESTERN U.S. ON FEB 27.



THE DETERMINISTIC 0Z ECMWF MODEL IS PREFERRED NEXT WEEK DUE TO ITS CONSISTENCY
DURING THE PAST TWO DAYS. LEE SIDE CYCLOGENESIS ON FEB 28 IS EXPECTED TO
PROMOTE HIGH WINDS (SPEEDS ABOVE 35 KNOTS) AND CRITICAL FIRE WEATHER CONDITIONS
ACROSS THE CENTRAL AND SOUTHERN HIGH PLAINS. ALTHOUGH MODERATE TO POTENTIALLY
HEAVY SNOW (4 TO 8 INCHES) IS EXPECTED ALONG THE NORTHWEST SIDE OF A SURFACE
LOW TRACKING ACROSS THE UPPER MISSISSIPPI VALLEY ON FEB 28 AND MAR 1,
CONFIDENCE IS TEMPERED DUE TO SPREAD AMONG DETERMINISTIC MODEL RUNS.  ROBUST
GULF INFLOW IS FORECAST TO RESULT IN HEAVY RAINFALL (48-HOUR TOTALS LOCALLY
EXCEEDING 2 INCHES) ACROSS THE OHIO AND TENNESSEE VALLEYS AND CENTRAL
APPALACHIANS ON FEB 28 AND MAR 1. SEVERE WEATHER IS ALSO POSSIBLE ACROSS THESE
SAME AREAS, BUT LOW PREDICTABILITY PRECLUDES DESIGNATION OF A SEVERE WEATHER
HAZARD AT THIS TIME.



THE LATEST MODEL GUIDANCE INDICATES A WEAKER LOW PRESSURE SYSTEM CROSSING THE
BERING SEA THIS WEEKEND WITH LOWER PRECIPITATION AMOUNTS. THEREFORE, THE HEAVY
SNOW HAZARDS ACROSS ALASKA FROM PREVIOUS OUTLOOKS ARE REMOVED. ARCTIC HIGH
PRESSURE IS FORECAST TO BUILD INTO THE NORTHERN TWO-THIRDS OF ALASKA. MUCH
BELOW-NORMAL TEMPERATURES ARE POSTED FOR EASTERN INTERIOR ALASKA WHERE THE 6Z
GFS ENSEMBLE MEAN INDICATES TEMPERATURES AVERAGING MORE THAN 20 DEGREES F BELOW
NORMAL.

FOR FRIDAY MARCH 03 - THURSDAY MARCH 09: THE LATEST ENSEMBLE MEANS INDICATE A
LARGE CHANGE IN THE LONGWAVE PATTERN ACROSS NORTH AMERICA DURING WEEK-2
COMPARED TO THE PREVIOUS FEW DAYS OF MODEL RUNS. 500-HPA HEIGHTS ARE NOW
FORECAST TO INCREASE (DECREASE) ACROSS THE WESTERN (EASTERN) U.S. DURING EARLY
MARCH. GIVEN THIS LARGE CHANGE IN TODAY`S MODELS RUNS, THE RISK FOR MUCH
BELOW-NORMAL TEMPERATURES IS REDUCED TO LOW ACROSS THE NORTHWESTERN U.S. AND
LIMITED TO ONLY MAR 3 AND 4. A SLIGHT TO MODERATE RISK OF MUCH BELOW-NORMAL
TEMPERATURES REMAINS MORE LIKELY ACROSS PARTS OF ALASKA DUE TO THE AMPLIFIED
RIDGE UPSTREAM OVER THE WESTERN BERING SEA. THERE ARE SIGNS IN THE LATEST
ENSEMBLE MEANS AND DETERMINISTIC MODEL RUNS THAT THE EVOLVING LONGWAVE PATTERN
MAY BECOME MORE CONDUCIVE FOR MUCH COLDER TEMPERATURES TO SHIFT SOUTH FROM
CANADA INTO PARTS OF THE CENTRAL AND EASTERN U.S. DURING EARLY MARCH.



THE AMPLIFYING RIDGE NEAR THE WEST COAST IS EXPECTED TO RESULT IN A MAJOR
PATTERN CHANGE WITH BELOW-MEDIAN PRECIPITATION FAVORED FOR CALIFORNIA DURING
WEEK-2.



ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON FEBRUARY 21, SEVERE DROUGHT IS
DESIGNATED ACROSS PARTS OF CALIFORNIA, ARIZONA, THE GREAT PLAINS, ARKANSAS,
SOUTH TEXAS, AND THE EASTERN U.S. COVERAGE OF SEVERE, OR GREATER INTENSITY,
DROUGHT THROUGHOUT THE CONTINENTAL U.S. REMAINED NEARLY STEADY AT 3.31 PERCENT.
CALIFORNIA, TO THE NORTH OF POINT CONCEPTION, IS FREE OF LONG-TERM SEVERE
DROUGHT.

FORECASTER: BRAD PUGH

$$




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