Prognostic Meteorological Discussion
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860
FXUS21 KWNC 201924
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 20 2017

SYNOPSIS: A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO LIFT FROM THE SOUTHERN
PLAINS THROUGH THE GREAT LAKES DURING THE FIRST HALF OF WEEK-1. BEHIND THIS
SYSTEM, SURFACE HIGH PRESSURE IS ANTICIPATED TO BUILD. DYNAMICAL MODELS ARE
INCONSISTENT LATER IN WEEK-1, BUT INDICATE THE POTENTIAL FOR A SECOND SURFACE
DISTURBANCE TO DEVELOP ACROSS THE SOUTHWEST LATE IN WEEK-1 THAT COULD SHIFT
INTO THE NORTHEAST BY THE END OF WEEK-1. PERIODIC SURFACE LOW PRESSURE SYSTEMS
ARE ANTICIPATED IN THE BERING SEA THROUGHOUT WEEK-1. SHIFTING TO WEEK-2,
MID-LEVEL LOW PRESSURE IS GENERALLY ANTICIPATED ACROSS THE WESTERN U.S., WITH
HIGH PRESSURE OVER THE EAST.

HAZARDS

HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE NORTHERN AND CENTRAL
PLAINS, THE UPPER MISSISSIPPI VALLEY, AND THE GREAT LAKES, THU-FRI, FEB 23-FEB
24.

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

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

HIGH WINDS ACROSS PORTIONS OF THE UPPER AND MIDDLE MISSISSIPPI VALLEY, THE
GREAT LAKES, THE NORTHERN PLAINS, AND THE OHIO VALLEY, FRI, FEB 24.

ENHANCED WILDFIRE RISK ACROSS PORTIONS OF THE THE SOUTHERN ROCKIES, THE
SOUTHERN PLAINS, AND THE SOUTHWEST, THU, FEB 23.

HIGH WINDS ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE SOUTHERN ROCKIES, THE
SOUTHERN PLAINS, AND THE SOUTHWEST, THU, FEB 23.

FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, THE GREAT LAKES,
CALIFORNIA, THE UPPER AND MIDDLE MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS.

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

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

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

HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALEUTIANS, THU-SAT,
FEB 23-25.

MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN
AND CENTRAL GREAT BASIN, THE NORTHERN AND CENTRAL ROCKIES, CALIFORNIA, AND THE
PACIFIC NORTHWEST, TUE-THU, FEB 28-MAR 2.

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, TUE-MON, FEB 28-MAR 6.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA
PANHANDLE AND MAINLAND ALASKA, WED-MON, MAR 1-6.

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 THURSDAY FEBRUARY 23 - MONDAY FEBRUARY 27: LEE CYCLOGENESIS IS ANTICIPATED
NEAR THE OKLAHOMA PANHANDLE AROUND THE BEGINNING OF THE FORECAST PERIOD. THE
SURFACE LOW IS FORECAST TO TRACK NORTHEASTWARD INTO THE GREAT LAKES BY THE
MIDDLE OF WEEK-1. ON THE BACK SIDE OF THIS SYSTEM, HEAVY SNOW (3" OR GREATER
TOTALS IN 24 HOURS) IS FORECAST ASSOCIATED WITH THE WRAP-AROUND REGION
STRETCHING FROM THE CENTRAL ROCKIES THROUGH THE NORTHERN/CENTRAL PLAINS AND
UPPER MISSISSIPPI VALLEY INTO THE NORTHERN GREAT LAKES ON FEB 23-24. THE STORM
PREDICTION CENTER GIVES A 15% CHANCE OF SEVERE WEATHER FURTHER SOUTH ACROSS THE
MIDWEST AND OHIO VALLEY ON FEB 24, WHERE POTENTIAL SQUALL LINE DEVELOPMENT
ASSOCIATED WITH THE COLD FRONTAL PASSAGE COULD YIELD SEVERE WINDS. HIGH WINDS
(SUSTAINED VALUES EXCEEDING 35 MPH) ARE FORECAST FOR MUCH OF THE UPPER AND
MIDDLE MISSISSIPPI VALLEY AND WESTERN GREAT LAKES ON FEB 24, ASSOCIATED WITH
THE TIGHT PRESSURE GRADIENT AROUND THE DEEPENING LOW. A REGION OF HEAVY RAIN
(EXCEEDING 1" IN 24 HOURS) IS ALSO POSSIBLE ACROSS THE UPPER MISSISSIPPI VALLEY
AND GREAT LAKES ON FEB 24.



AS THE AFOREMENTIONED DISTURBANCE POTENTIALLY STRENGTHENS IN THE PLAINS, A
REGION OF ASSOCIATED HIGH WINDS IS POSSIBLE TO ACROSS THE CENTRAL AND SOUTHERN
ROCKIES ALONG WITH THE SOUTHERN PLAINS AND SOUTHWEST ON FEB 23. HERE THERE ALSO
EXISTS ENHANCED POTENTIAL FOR FIRE WEATHER DUE TO THE ANTICIPATED DRY,
DOWNSLOPE WINDS IN CONJUNCTION WITH DRY FUEL PRESENCE ON FEB 23. IT SHOULD BE
NOTED THE FIRE WEATHER RISK WILL BE ENHANCED TO A LESSER DEGREE ACROSS A
BROADER REGION FROM THE SOUTHWEST THROUGH THE SOUTHERN PLAINS FOR FEB 23-25,
ALTHOUGH NOT PRESENTLY FAVORED TO MEET HAZARD CRITERIA.



LATE IN WEEK-1 THE GFS AND ECMWF MODEL SUITES DIVERGE SUBSTANTIALLY IN REGARDS
TO A POTENTIAL SECOND LEE CYCLOGENESIS SYSTEM. THE 0Z AND 12Z OPERATIONAL GFS
EJECTS A SECOND SHORT WAVE OUT OF THE SOUTHERN ROCKIES ON FEB 26 THAT IS
FORECASTS TO DEEPEN WHILE TRACKING TOWARD THE MID-ATLANTIC BY THE END OF
WEEK-1. SOME 12Z GEFS MEMBERS FEATURE THIS DISTURBANCE, BUT GENERALLY FAVOR A
TRACK FURTHER WEST TOWARDS THE GREAT LAKES.  EITHER OF THE GFS-BASED SOLUTIONS
WOULD RESULT IN A REGION OF HIGH WINDS ACROSS NEW MEXICO INTO WEST TEXAS ON FEB
26, AND HEAVY RAIN AND SNOW ALONG THE CYCLONE TRACK. HOWEVER, 0Z OPERATIONAL
ECMWF AND ECENS GUIDANCE DO NOT SUPPORT DEVELOPMENT OF THIS SYSTEM, WITH THE
RESULTING UNCERTAINTY CAUSING NO HAZARDS TO BE FORECAST. SUBSEQUENT OUTLOOKS
WILL MONITOR CONSISTENCY AMONG MODEL SOLUTIONS BEFORE CONSIDERING ANY POSSIBLE
HAZARDOUS IMPACTS.



A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO DEEPEN IN THE BERING SEA NEAR THE
BEGINNING OF THE FORECAST PERIOD. PERSISTENT SOUTHERLY WINDS WITH THIS SYSTEM
ARE FORECAST TO IMPACT THE ALEUTIANS, WITH SIGNIFICANT WAVES (EXCEEDING 20`) TO
THE WINDWARD COASTLINES FEB 23-25. HAZARDOUS HIGH WINDS (APPROACHING 50 KT) ARE
FORECAST TO IMPACT THE WESTERN ALEUTIANS ON FEB 24.

FOR TUESDAY FEBRUARY 28 - MONDAY MARCH 06: A HIGH AMPLITUDE 500-HPA PATTERN IS
ANTICIPATED DURING WEEK-2, WITH ANOMALOUS RIDGING IN THE NORTH PACIFIC AND
ALONG THE ATLANTIC COAST SPLIT BY ANOMALOUS TROUGHING THROUGH THE ROCKIES. THIS
SCENARIO FAVORS POTENTIAL BELOW-NORMAL TEMPERATURES FOR MUCH OF THE WEST, WITH
THE HIGHEST ODDS APPEARING EARLY IN WEEK-2 WHERE A MORE NORTHERLY COMPONENT TO
THE LOW-LEVEL FLOW IS FORECAST. A MODERATE RISK OF MUCH BELOW-NORMAL
TEMPERATURES EXISTS BETWEEN THE PACIFIC COASTLINE AND ROCKY MOUNTAINS AS FAR
SOUTH AS NORTHERN CALIFORNIA FOR FEB 28-MAR 2. HERE THE GEFS PROBABILISTIC
EXTREMES TOOL INDICATES A 40% OR HIGHER CHANCE OF MINIMUM TEMPERATURES BEING
BELOW THE 15TH CLIMATOLOGICAL PERCENTILE, WHILE THE ECENS HAS A SIMILARLY COLD
FORECAST. THE GEFS TOOL INDICATES A BROAD AREA FROM THE PACIFIC COAST THROUGH
THE GREAT PLAINS WHERE A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS
POSSIBLE FEB 28 - MAR 6.



A NUMBER OF DISTURBANCES ARE FORECAST IN THE GULF OF ALASKA AND BERING SEA
DURING WEEK-2 BY DYNAMICAL MODEL GUIDANCE. OUTSIDE OF THE ALEUTIANS, SOUTHERN
COAST, AND PANHANDLE MUCH OF THE STATE IS FAVORED TO SEE DRY WEATHER. A SLIGHT
RISK OF MUCH BELOW-NORMAL TEMPERATURES IS FORECAST FOR THE ALASKA PANHANDLE
DURING MARCH 1-6 ASSOCIATED WITH SURFACE HIGH PRESSURE FORECAST TO SETTLE OVER
THE YUKON.



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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