Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 192019
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST FEBRUARY 19 2018

SYNOPSIS: AT THE START OF THE PERIOD, A STATIONARY FRONTAL SYSTEM IS EXPECTED
TO STRETCH FROM EASTERN TEXAS NORTHEASTWARD ACROSS THE LOWER MISSISSIPPI,
TENNESSEE AND OHIO VALLEYS TO THE EASTERN GREAT LAKES. COLD SURFACE HIGH
PRESSURE IS FORECAST OVER THE NORTHWESTERN AND NORTH-CENTRAL PARTS OF THE
NATION. AREAS OF MID-LEVEL LOW PRESSURE ARE ANTICIPATED TO MOVE ACROSS THE
NORTHWEST U.S. FEB 23-25. HIGH PRESSURE IS FORECAST OVER THE GULF OF ALASKA
WHILE FRONTAL SYSTEMS ARE EXPECTED TO CROSS THE ALEUTIANS FEB 22-26. DURING
WEEK-2, MID-LEVEL LOW PRESSURE IS PREDICTED OVER THE WESTERN U.S., WHILE AREAS
OF MID-LEVEL HIGH PRESSURE ARE ANTICIPATED OVER WESTERN ALASKA/THE ALEUTIANS
AND THE EAST-CENTRAL U.S.

HAZARDS

HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, THE LOWER AND MIDDLE
MISSISSIPPI VALLEYS, THE CENTRAL AND SOUTHERN APPALACHIANS, THE TENNESSEE AND
OHIO VALLEYS, AND THE GREAT LAKES, THU-SUN, FEB 22-FEB 25.

SEVERE WEATHER POSSIBLE FOR PARTS OF THE SOUTHERN PLAINS, AND LOWER MISSISSIPPI
AND TENNESSEE VALLEYS, SAT, FEB 24.

HEAVY SNOW FOR PARTS OF THE CASCADES, FRI-SUN, FEB 23-25.

HEAVY SNOW FOR PARTS OF THE BITTERROOTS, NORTHERN ROCKIES, AND BLUE MOUNTAINS,
SAT-SUN, FEB 24-25.

PERIODS OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC NORTHWEST,
CALIFORNIA, GREAT BASIN, NORTHERN AND CENTRAL ROCKIES, SOUTHWEST, NORTHERN
PLAINS, AND UPPER MISSISSIPPI VALLEY, THU-MON, FEB 22-26.

HIGH WINDS FOR PARTS OF COASTAL SECTIONS OF NORTHERN AND CENTRAL CALIFORNIA,
THU-FRI, FEB 22-23.

MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, THU, FEB 22.

HIGH WINDS FOR PARTS OF THE ALASKA PENINSULA, SOUTHWESTERN AND SOUTH COASTAL
MAINLAND ALASKA, KODIAK ISLAND, AND THE KENAI PENINSULA, THU-FRI, FEB 22-23.

PERIODS OF HIGH WINDS FOR PARTS OF THE ALEUTIANS, FRI-SUN, FEB 23-25.

PERIODS OF HIGH SIGNIFICANT WAVE HEIGHTS FOR PARTS OF THE ALEUTIANS, FRI-MON,
FEB 23-26.

FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHERN PLAINS, MISSISSIPPI VALLEY,
THE OHIO VALLEY AND GREAT LAKES.

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE WESTERN AND
NORTH-CENTRAL CONUS, TUE-MON, FEB 27-MAR 5.

MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE PACIFIC
NORTHWEST, NORTHERN CALIFORNIA, GREAT BASIN, NORTHERN AND CENTRAL ROCKIES, AND
NORTHERN AND CENTRAL PLAINS, TUE-MON, FEB 27-MAR 5.

HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN ROCKIES
AND NORTHERN PLAINS, TUE-WED, FEB 27-28.

SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF SOUTHERN CALIFORNIA AND THE
SOUTHWEST, TUE-SAT, FEB 27-MAR 3.

MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF SOUTHERN CALIFORNIA AND
THE SOUTHWEST, TUE-SAT, FEB 27-MAR 3.

SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS,
TUE-THU, FEB 27-MAR 1.

MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS,
TUE-THU, FEB 27-MAR 1.

SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE CENTRAL ROCKIES, THE LOWER
MISSISSIPPI VALLEY, THE CENTRAL GREAT BASIN, THE NORTHERN PLAINS, THE SOUTHERN
ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, CALIFORNIA, THE SOUTHERN PLAINS, AND
THE SOUTHWEST.

DETAILED SUMMARY

FOR THURSDAY FEBRUARY 22 - MONDAY FEBRUARY 26: AT THE START OF THE PERIOD, A
VERY SLOW MOVING FRONTAL SYSTEM IS FORECAST TO STRETCH FROM EAST TEXAS
NORTHEASTWARD TO THE LOWER MISSISSIPPI, TENNESSEE AND OHIO VALLEYS. AREAS OF
LOW PRESSURE ARE EXPECTED TO RIPPLE ALONG THE FRONT CAUSING HEAVY RAIN (AMOUNTS
IN EXCESS OF 1 INCH IN 24 HOURS) ACROSS PORTIONS OF THE SOUTHERN PLAINS, THE
LOWER AND MIDDLE MISSISSIPPI VALLEYS, THE CENTRAL AND SOUTHERN APPALACHIANS,
THE TENNESSEE AND OHIO VALLEYS, AND THE GREAT LAKES FEB 22-25. IN ADDITION,
SEVERE WEATHER IS POSSIBLE FOR PARTS OF THE SOUTHERN PLAINS, AND LOWER
MISSISSIPPI AND TENNESSEE VALLEYS FEB 24.



SNOW MELT AND HEAVY RAINFALL DURING THE PERIOD ON AREAS THAT HAVE FROZEN GROUND
LEAD TO POSSIBLE RIVER FLOODING ACROSS PORTIONS OF THE SOUTHERN PLAINS,
MISSISSIPPI VALLEY, THE OHIO VALLEY AND GREAT LAKES.



AREAS OF HIGH PRESSURE OVER THE GREAT BASIN ARE EXPECTED TO MOVE EASTWARD TO
THE NORTH-CENTRAL CONUS. OFFSHORE FLOW LEADS TO HIGH WINDS (SPEEDS IN EXCESS OF
30 KNOTS) FOR PARTS OF COASTAL SECTIONS OF NORTHERN AND CENTRAL CALIFORNIA FEB
22-23. THE AREAS OF HIGH PRESSURE RESULT IN PERIODS OF MUCH-BELOW NORMAL
TEMPERATURES (NEGATIVE ANOMALIES OF 20-25 DEGREES F) FOR PARTS OF THE PACIFIC
NORTHWEST, CALIFORNIA, GREAT BASIN, NORTHERN AND CENTRAL ROCKIES, SOUTHWEST,
NORTHERN PLAINS, AND UPPER MISSISSIPPI VALLEY FEB 22-26.



AREAS OF MID-LEVEL LOW PRESSURE ARE FORECAST TO CROSS THE NORTHWEST CONUS.
HEAVY SNOW (AMOUNTS IN EXCESS OF 6 INCHES IN 24 HOURS) IS FORECAST FOR PARTS OF
THE CASCADES FEB 23-25, AND PARTS OF THE BITTERROOTS, NORTHERN ROCKIES, AND
BLUE MOUNTAINS FEB 24-25.



HIGH PRESSURE OVER THE GULF OF ALASKA LEADS TO STRONG SOUTHERLY FLOW ACROSS
MUCH OF THE STATE. MUCH ABOVE NORMAL TEMPERATURES (POSITIVE TEMPERATURE
ANOMALIES OF 20-30 DEGREES F) ARE EXPECTED ACROSS PORTIONS OF MAINLAND ALASKA
FEB 22. THE TIGHT PRESSURE GRADIENT BETWEEN THE AREA OF HIGH PRESSURE AND LOW
PRESSURE OVER THE BERING SEA IS PREDICTED TO CAUSE HIGH WINDS (SPEEDS IN EXCESS
OF 40 KNOTS) FOR PARTS OF THE ALASKA PENINSULA, SOUTHWESTERN AND SOUTH COASTAL
MAINLAND ALASKA, KODIAK ISLAND, AND THE KENAI PENINSULA FEB 22-23.  A SERIES OF
FRONTAL SYSTEMS CROSSING THE ALEUTIANS LEADS TO PERIODS OF HIGH WINDS (SPEEDS
IN EXCESS OF 40 KNOTS) FEB 23-25, AND HIGH SIGNIFICANT WAVE HEIGHTS (IN EXCESS
OF 20 FEET) FEB 23-26.

FOR TUESDAY FEBRUARY 27 - MONDAY MARCH 05: THE WEEK-2 MID-LEVEL FLOW PATTERN
ACROSS THE FORECAST DOMAIN IS EXPECTED TO FEATURE A

TROUGH OVER THE WESTERN CONUS AND RIDGES OVER WESTERN ALASKA/THE ALEUTIANS AND
THE EAST-CENTRAL CONUS. A ROBUST SOUTHERN JET STREAM IS FORECAST ACROSS THE
SOUTHERN TIER OF THE U.S. BELOW NORMAL HEIGHTS LEAD TO A SLIGHT RISK OF MUCH
BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE WESTERN AND NORTH-CENTRAL CONUS
FEB 27-MAR 5, A MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF
THE PACIFIC NORTHWEST, NORTHERN CALIFORNIA, GREAT BASIN, NORTHERN AND CENTRAL
ROCKIES, AND NORTHERN AND CENTRAL PLAINS FEB 27-MAR 5, AND A HIGH RISK OF MUCH
BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN ROCKIES AND NORTHERN PLAINS
FEB 27-28.



THE TROUGH OVER THE WESTERN CONUS IS EXPECTED TO CAUSE A SLIGHT RISK OF HEAVY
PRECIPITATION FOR PORTIONS OF SOUTHERN CALIFORNIA AND THE SOUTHWEST FEB 27-MAR
3, A MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF SOUTHERN CALIFORNIA
AND THE SOUTHWEST FEB 27-MAR 3, A SLIGHT RISK OF HEAVY PRECIPITATION FOR
PORTIONS OF THE SOUTHERN PLAINS FEB 27-MAR 1, AND A MODERATE RISK OF HEAVY
PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS FEB 27-MAR 1.



THE U.S. DROUGHT MONITOR, VALID ON FEB 13, 2018 INDICATES A SLIGHT DECREASE IN
THE COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2-D4) FROM 18.44% LAST WEEK TO
18.04% THIS WEEK. A FEW OF THE MORE SUBSTANTIAL REVISIONS MADE TO THE MAP THIS
WEEK INCLUDE AN INCREASE IN D2 COVERAGE ACROSS SOUTHERN CALIFORNIA, THE
ELIMINATION OF ALL D2 AREAS ACROSS THE GULF COAST STATES FROM LOUISIANA TO
FLORIDA, AND SIGNIFICANT 1-CATEGORY IMPROVEMENTS RENDERED ACROSS THE CAROLINAS,
MID-ATLANTIC, AND NORTHEAST.

FORECASTER: RANDY SCHECHTER

$$




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