Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 212012
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 21 2017

SYNOPSIS: A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO LIFT FROM THE MIDDLE
MISSISSIPPI VALLEY INTO ONTARIO EARLY IN THE OUTLOOK PERIOD. BY THE MIDDLE OF
THE OUTLOOK PERIOD, A DISTURBANCE IS ANTICIPATED TO APPROACH CALIFORNIA FROM
THE PACIFIC. DYNAMICAL MODEL GUIDANCE CONTINUES TO DISAGREE REGARDING THE
POSSIBILITY OF A SURFACE LOW PRESSURE SYSTEM FORMING DOWNSTREAM OF THE ROCKIES
TOWARDS THE END OF WEEK-1. A STRONG LOW PRESSURE SYSTEM IS FORECAST IN THE
BERING SEA DURING THE FIRST HALF OF WEEK-1. MID-LEVEL LOW PRESSURE IS GENERALLY
FORECAST ACROSS THE WEST DURING WEEK-2, WITH MID-LEVEL HIGH PRESSURE FAVORED
FOR THE EAST.

HAZARDS

SEVERE WEATHER ACROSS PORTIONS OF THE GREAT LAKES AND THE OHIO VALLEY, FRI, FEB
24.

HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER MISSISSIPPI VALLEY,
FRI, FEB 24.

HEAVY PRECIPITATION ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, CALIFORNIA, AND
THE SOUTHWEST, SAT-MON, FEB 25-FEB 27.

HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES AND THE CENTRAL
GREAT BASIN, MON, FEB 27.

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

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE CENTRAL GREAT BASIN AND
CALIFORNIA.

FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN AND CENTRAL GREAT BASIN,
CALIFORNIA, AND THE NORTHERN ROCKIES.

HEAVY SNOW ACROSS PORTIONS OF NORTHWEST ALASKA, SAT, FEB 25.

HIGH WINDS ACROSS PORTIONS OF THE WESTERN ALEUTIANS, FRI, FEB 24.

HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE WESTERN ALEUTIANS,
FRI, FEB 24.

HEAVY RAIN ACROSS FOR PORTIONS OF THE SOUTHEAST AND OHIO, TENNESSEE, AND LOWER
MISSISSIPPI VALLEYS, WED, MAR 1.

MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN
AND CENTRAL PLAINS, THE NORTHERN AND CENTRAL GREAT BASIN, THE NORTHERN AND
CENTRAL ROCKIES, CALIFORNIA, AND THE PACIFIC NORTHWEST, FRI-TUE, MAR 3-MAR 7.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT PLAINS,
THE ROCKIES, THE GREAT BASIN, CALIFORNIA, THE PACIFIC NORTHWEST, AND THE
SOUTHWEST, WED-TUE, MAR 1-MAR 7.

MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA
PANHANDLE AND MAINLAND ALASKA, WED-SAT, MAR 1-MAR 4.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA
PANHANDLE AND MAINLAND ALASKA, WED-SUN, MAR 1-MAR 5.

SEVERE DROUGHT ACROSS 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.

DETAILED SUMMARY

FOR FRIDAY FEBRUARY 24 - TUESDAY FEBRUARY 28: A DEEPENING LOW IS FORECAST TO BE
IN THE VICINITY OF THE MIDDLE MISSISSIPPI VALLEY AS THE OUTLOOK PERIOD BEGINS.
HEAVY SNOW (EXCEEDING 4" IN 24 HOURS) CONTINUES TO BE FORECAST ALONG THE
SYSTEM`S NORTHWEST SIDE ASSOCIATED WITH THE WRAP AROUND REGION, STRETCHING FROM
NORTH-CENTRAL IOWA THROUGH THE UPPER PENINSULA OF MICHIGAN ON FEB 24. THE STORM
PREDICTION CENTER INDICATES A 15% CHANCE OF SEVERE WEATHER IN THE WARM SECTOR
OF THE SYSTEM ACROSS PARTS OF THE MIDWEST AND OHIO VALLEY ON FEB 24.
ANTICIPATED LINEAR SHEAR PROFILES AND MARGINAL INSTABILITY FAVOR SEVERE WINDS
AS THE PRIMARY THREAT ACROSS THIS REGION. TODAY`S MODEL GUIDANCE INDICATES A
SLIGHTLY MORE PROGRESSIVE TRACK AND LESS DEEPENING OF THE SYSTEM ACROSS THE
MIDWEST RELATIVE TO YESTERDAY, RESULTING IN DISCONTINUATION OF HIGH WIND AND
HEAVY RAINFALL HAZARDS TIED TO THIS LOW THAT WERE IN THE PREVIOUS OUTLOOK.



NORTHWESTERLY WINDS ARE FORECAST ACROSS NEW MEXICO AND WEST TEXAS IN THE WAKE
OF THE AFOREMENTIONED SYSTEM. THIS DOWNSLOPE WIND SCENARIO WOULD SUPPORT WARM
AND DRY CONDITIONS ACROSS THE AREA THAT COULD ELEVATE FIRE WEATHER CONCERNS ON
FEB 24-25. CONFIDENCE IN THESE FIRE WEATHER CONDITIONS REACHING CRITICAL STATUS
IS INSUFFICIENT TO HIGHLIGHT A HAZARDOUS AREA ON THE OUTLOOK GRAPHIC.



ANOTHER SURFACE LOW PRESSURE IS FORECAST TO APPROACH CALIFORNIA FROM THE
PACIFIC BY THE MIDDLE OF WEEK-1. ASSOCIATED WITH THIS SYSTEM, HEAVY
PRECIPITATION (LIQUID EQUIVALENT OF 2" OR MORE IN 24 HOURS, WITH HIGH ELEVATION
SNOW AND RAIN ELSEWHERE) IS FORECAST FOR FEB 25-27. THE INITIAL FAVORED HAZARD
IS UPSLOPE HEAVY SNOWFALL IN THE NORTHERN COAST RANGES AND SIERRAS (ABOVE 5000
FT) ASSOCIATED WITH MOIST, SOUTHERLY FLOW AHEAD OF THE SYSTEM. BY FEB 26 THE
PRIMARY SURGE OF MOISTURE IS ANTICIPATED INTO CALIFORNIA, WITH HEAVY
PRECIPITATION FOR MUCH OF THE AREA INDICATED ON THE MAP. HEAVY SNOW IS
ANTICIPATED TO LINGER ACROSS THE HIGHER ELEVATIONS ON FEB 27, WHERE UP TO 2` IS
POSSIBLE THROUGHOUT THE FULL STORM DURATION. ACROSS THE INTERIOR OF THE WEST,
HEAVY UPSLOPE SNOW WITH THIS SYSTEM IS POSSIBLE ACROSS SOUTHWESTERN FACING
SLOPES OF THE NORTHERN AND CENTRAL ROCKIES AND CENTRAL GREAT BASIN ON FEB 27,
WHERE UP TO A FOOT OF SNOWFALL IS POSSIBLE.



DISCREPANCIES CONTINUE ACROSS THE EASTERN HALF OF THE CONUS LATE IN WEEK-1,
WITH THE OPERATIONAL GFS AND SOME GEFS MEMBERS CONTINUING TO FORECAST LEE
CYCLOGENESIS OVER THE CENTRAL PLAINS WITH THE SYSTEM THEN TRACKING TOWARDS THE
GREAT LAKES. SOME ECMWF ENSEMBLE MEMBERS HAVE BEGUN TO SHOW A SIMILAR SOLUTION,
BUT THE OPERATIONAL RUN LACKS THIS FEATURE. MORE CONSISTENCY IS SOUGHT AMONG
DYNAMICAL MODEL GUIDANCE BEFORE ANY HAZARDS CAN BE CONSIDERED.



A DEEP LOW PRESSURE SYSTEM IS FORECAST IN THE BERING SEA EARLY IN WEEK-1. HIGH
WINDS (EXCEEDING 50 KT) OUT OF THE SOUTHWEST COULD HELP DRIVE SIGNIFICANT WAVE
HEIGHTS (EXCEEDING 20`) ON THE WINDWARD SHORES OF THE WESTERN ALEUTIANS ON FEB
24. THIS DISTURBANCE IS FORECAST TO PUSH EASTWARD AND BEGIN IMPACTING THE
WESTERN COAST OF MAINLAND ALASKA, WITH HEAVY SNOW POSSIBLE FROM THE SEWARD
PENINSULA NORTHWARD TOWARDS THE NORTH SLOPE ON FEB 25. 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.

FOR WEDNESDAY MARCH 01 - TUESDAY MARCH 07: WEEK-2 CONTINUES TO FAVOR A
HIGH-AMPLITUDE 500-HPA FORECAST PATTERN WITH ANOMALOUS RIDGING IN THE NORTH
PACIFIC AND EASTERN CONUS, AND TROUGHING OVER THE WESTERN CONUS. THIS SETUP
FAVORS MUCH BELOW-NORMAL TEMPERATURES STRETCHING FROM SOUTHEASTERN ALASKA
THROUGH THE GREAT PLAINS. THE COLDEST AIR IS FORECAST FOR THE ALASKA PANHANDLE
AND PACIFIC NORTHWEST THROUGH NORTHERN ROCKIES. THE ALASKA PANHANDLE HAS A
MODERATE CHANCE OF MUCH BELOW-NORMAL TEMPERATURES FOR MAR 1-4, WITH A
MARGINALLY BROADER AREA HAVING A SLIGHT CHANCE OF BELOW-NORMAL TEMPERATURES MAR
1-5. APPROXIMATELY THE WESTERN HALF OF THE CONUS IS GIVEN A SLIGHT RISK OF MUCH
BELOW-NORMAL TEMPERATURES FOR THE ENTIRETY OF WEEK-2. THE NORTHWESTERN PORTION
OF THIS AREA IS GIVEN A MODERATE CHANCE OF MUCH BELOW-NORMAL TEMPERATURES MAR
3-7.



THE HIGH AMPLITUDE PATTERN ALSO FAVORS POTENTIAL CYCLOGENESIS DOWNSTREAM OF THE
ROCKIES DURING WEEK-2. BOTH THE GEFS AND ECENS ENSEMBLE MEANS SUGGEST A BROAD
REGION APPROACHING 1" OF PRECIPITATION CENTERED ON THE TENNESSEE VALLEY ON MAR
1. CFS SEVERE WEATHER GUIDANCE ALSO HINTS AT THE POTENTIAL FOR ACTIVITY IN THE
SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY LATE IN WEEK-1, BUT THE STORM
PREDICTION CENTER CITES PREDICTABILITY LIMITATIONS IN NOT TARGETING A SPECIFIC
HAZARD AT PRESENT.



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: DANIEL HARNOS

$$



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