Prognostic Meteorological Discussion
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443
FXUS21 KWNC 221928
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 22 2017

SYNOPSIS: A STRONG SURFACE LOW IS FORECAST TO EXIT THE GREAT LAKES ON SATURDAY,
FEB 25. ANOTHER VIGOROUS LOW PRESSURE SYSTEM IS EXPECTED TO MOVE INLAND INTO
THE WESTERN U.S. BY EARLY NEXT WEEK. SURFACE LOW DEVELOPMENT IS FORECAST TO
DEVELOP ACROSS THE CENTRAL GREAT PLAINS ON TUESDAY, FEB 28 WITH A SUBSEQUENT
TRACK NORTHEAST TO THE GREAT LAKES. A LOW PRESSURE SYSTEM IS FORECAST TO CROSS
THE BERING SEA EARLY IN THE PERIOD. DURING WEEK-2, AN AREA OF UPPER-LEVEL LOW
PRESSURE IS FAVORED OVER THE WESTERN U.S. WHILE AN UNSEASONABLY STRONG AREA OF
UPPER-LEVEL HIGH PRESSURE REMAINS ANCHORED OVER THE SOUTHWEST ATLANTIC.

HAZARDS

HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR PARTS OF CALIFORNIA,
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.

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.

HEAVY SNOW FOR PARTS OF INTERIOR NORTHWEST ALASKA AND THE ALASKA RANGE,
SAT-SUN, FEB 25-26.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE WESTERN U.S.
AND PARTS OF THE NORTHERN AND CENTRAL GREAT PLAINS, THU-TUE, MAR 2-7.

A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC
NORTHWEST, NORTHERN GREAT BASIN, AND NORTHERN ROCKIES, THU-SUN, MAR 2-5.

A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE ALASKA PANHANDLE, MUCH
OF MAINLAND ALASKA, AND PARTS OF THE ALASKA PENINSULA, THU-WED, MAR 2-8.

A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF SOUTHEASTERN
MAINLAND ALASKA AND THE ALASKA PANHANDLE, THU-SUN, MAR 2-5.

FLOODING POSSIBLE ACROSS PORTIONS OF THE UPPER AND MIDDLE MISSISSIPPI VALLEY.

FLOODING OCCURRING, IMMINENT, OR LIKELY ACROSS PORTIONS OF CALIFORNIA, THE
GREAT BASIN, AND PACIFIC NORTHWEST.

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

DETAILED SUMMARY

FOR SATURDAY FEBRUARY 25 - WEDNESDAY MARCH 01: A POTENT SHORTWAVE TROUGH WITH
ENHANCED PACIFIC MOISTURE IS FORECAST TO ENTER CALIFORNIA WHERE HEAVY
PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) IS MOST LIKELY ACROSS THE SIERRA
MOUNTAINS ALONG WITH CENTRAL AND SOUTHERN CALIFORNIA. MODEL GUIDANCE INDICATES
PRECIPITATION AMOUNTS RANGING FROM 1 TO 3 INCHES, LIQUID EQUIVALENT, IN THE
OUTLINED HAZARD AREA ON FEBRUARY 26 AND 27. SNOW LEVELS ARE EXPECTED TO BE
RELATIVELY LOW OVER THE SIERRA MOUNTAINS. AS THE SHORTWAVE TROUGH PROGRESSES
INLAND OVER THE WESTERN U.S., HEAVY SNOW (6 INCHES OR MORE) IS FORECAST FOR THE
HIGHER ELEVATIONS OF ARIZONA AND THE COLORADO ROCKIES ON FEBRUARY 27 AND 28.
SNOW LEVELS ARE EXPECTED TO FALL BELOW 6,000 FEET ACROSS ARIZONA BY TUESDAY,
FEB 28 WITH LOWERING 500-HPA HEIGHTS. HIGH WINDS (SPEEDS ABOVE 35 KNOTS) ARE
FORECAST TO ACCOMPANY THE UPPER-LEVEL TROUGH OVER THE SOUTHWESTERN U.S. ON FEB
27 AND EXTEND TO THE CENTRAL AND SOUTHERN HIGH PLAINS ON FEB 28. THE RISK OF
CRITICAL FIRE WEATHER CONDITIONS RETURNS TO THE CENTRAL AND SOUTHERN HIGH
PLAINS EARLY NEXT WEEK AND ARE EXPECTED TO BE POSTED ON THE HAZARDS MAP LATER
THIS WEEK.



DETERMINISTIC MODEL SOLUTIONS FEATURE SURFACE LOW DEVELOPMENT ACROSS THE
CENTRAL GREAT PLAINS BY FEB 28. ALTHOUGH THERE REMAINS MODEL SPREAD ON THE
STRENGTH AND TRACK OF THIS SURFACE LOW AS IT MOVES TO THE GREAT LAKES, FORECAST
CONFIDENCE IS INCREASING FOR A SWATH OF HEAVY SNOW (4 TO 8 INCHES, POTENTIALLY
MORE) OVER THE UPPER MISSISSIPPI VALLEY ON FEB 28 AND MAR 1. THE DETERMINISTIC
ECMWF MODEL IS THE MOST BULLISH WITH THE STRENGTH OF THE SURFACE LOW.
MEANWHILE, IN THE WARM SECTOR, ROBUST GULF INFLOW SETS THE STAGE FOR HEAVY RAIN
(MORE THAN 1 INCH PER 24 HOURS) AHEAD AND ALONG A COLD FRONT ACROSS THE OHIO
AND TENNESSEE VALLEYS AND CENTRAL APPALACHIANS ON FEB 28 AND MAR 1. SEVERE
WEATHER IS ALSO POSSIBLE FOR THESE SAME AREAS, BUT MODEL VARIABILITY PRECLUDES
DESIGNATION OF A SEVERE WEATHER HAZARD AT THIS TIME.



A DEEP LOW PRESSURE SYSTEM IS FORECAST IN THE BERING SEA AT THE BEGINNING OF
WEEK-1 WITH HEAVY SNOW PREDICTED FOR NORTHWEST INTERIOR ALASKA. SUSTAINED WINDS
DO NOT APPEAR LIKELY TO MEET THE REGION`S HAZARD CRITERIA (35 KT), BUT PERIODIC
BLIZZARD CONDITIONS (FREQUENT GUSTS TO 35 MPH FOR 3 CONSECUTIVE HOURS) ARE
POSSIBLE WITH THIS SYSTEM. A SECOND AREA OF HEAVY SNOW (TOTAL AMOUNTS GREATER
THAN 12 INCHES) IS FORECAST FOR THE WESTERN AND NORTHERN SLOPES OF THE ALASKA
RANGE ON FEB 25 AND 26.

FOR THURSDAY MARCH 02 - WEDNESDAY MARCH 08: THE PREDICTED LONGWAVE PATTERN
DURING WEEK-2 CONTINUES TO FEATURE A HIGHLY AMPLIFIED RIDGE OVER THE NORTH
PACIFIC WITH A DOWNSTREAM TROUGH OVER WESTERN NORTH AMERICA. THIS UPPER-LEVEL
PATTERN FAVORS BELOW-NORMAL TEMPERATURES ACROSS ALASKA AND THE WESTERN U.S.
EARLY IN WEEK-2, THE HIGHEST ODDS FOR MUCH BELOW-NORMAL TEMPERATURES EXISTS
ACROSS SOUTHEAST MAINLAND ALASKA, THE ALASKA PANHANDLE, AND THE NORTHWESTERN
U.S. WHERE THE GEFS PROBABILISTIC EXTREMES TOOL INDICATES A 40 PERCENT OR
HIGHER CHANCE OF MINIMUM TEMPERATURES BELOW THE 15TH PERCENTILE COMPARED TO
CLIMATOLOGY.



THE AMPLIFIED RIDGE UPSTREAM ACROSS THE NORTH PACIFIC IS EXPECTED TO RESULT IN
A MAJOR PATTERN CHANGE WITH BELOW-MEDIAN PRECIPITATION FAVORED FOR CALIFORNIA
DURING EARLY MARCH.



SEVERE DROUGHT IS CURRENTLY NOTED OVER PORTIONS OF THE CENTRAL PLAINS, THE
MID-ATLANTIC, THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE
NORTHEAST, CALIFORNIA, THE SOUTHEAST, THE SOUTHERN APPALACHIANS, THE SOUTHERN
PLAINS, AND THE SOUTHWEST. COVERAGE OF SEVERE, OR GREATER INTENSITY, DROUGHT
DECREASED TO 3.17 PERCENT OF THE CONUS. THIS IS THE LOWEST COVERAGE OF SEVERE
TO EXCEPTIONAL DROUGHT SINCE OCTOBER 2010.

FORECASTER: BRAD PUGH

$$




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