Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
000
FXUS21 KWNC 152048
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 15 2017

SYNOPSIS: A COLD FRONT IS FORECAST TO MOVE ACROSS THE GREAT LAKES DURING THE
MIDDLE OF NEXT WEEK. SOUTH OF THIS FRONT, A LOW-PRESSURE SYSTEM IS FORECAST TO
SPIN-UP OVER THE LOWER MISSISSIPPI VALLEY. LATER IN THE WEEK, A LOW-PRESSURE
SYSTEM IS FORECAST TO MOVE FROM THE PACIFIC NORTHWEST TO THE GREAT PLAINS AND
EVENTUALLY THE GREAT LAKES BY NEXT WEEKEND, BRINGING ACTIVE WEATHER ALONG THAT
ENTIRE TRACK. A STORMY PATTERN IS PREDICTED FOR WESTERN AND SOUTHERN ALASKA.

HAZARDS

HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST, TUE, DEC 19.

HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE SOUTHERN APPALACHIANS, THE
LOWER MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE TENNESSEE VALLEY,
MON-TUE, DEC 18-DEC 19.

HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND THE NORTHERN ROCKIES,
MON-TUE, DEC 18-DEC 19.

HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES, WED-THU, DEC 20-DEC 21.

HIGH WINDS ACROSS PORTIONS OF SOUTHERN CALIFORNIA, THU-FRI, DEC 21-DEC 22.

HIGH WINDS ACROSS PORTIONS OF THE GREAT LAKES, THE OHIO VALLEY, THE NORTHEAST,
AND THE MID-ATLANTIC, , TUE-WED, DEC 19-DEC 20.

HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND
ALASKA, FRI, DEC 22.

HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS, MON, DEC 18.

MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, THU-FRI, DEC
21-DEC 22.

HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALEUTIANS, MON-TUE,
DEC 18-DEC 19.

FROZEN PRECIPITATION IS LIKELY ALONG THE HIGH PLAINS, FROM MONTANA TO COLORADO,
SAT-SUN,DEC 23-24.

FROZEN PRECIPITATION IS LIKELY FROM THE LOWER MISSISSIPPI VALLEY TO THE
SOUTHERN APPALACHIANS, SAT-SUN, DEC 23-24

SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL
PLAINS, THE CENTRAL ROCKIES, THE MID-ATLANTIC, THE LOWER MISSISSIPPI VALLEY,
THE CENTRAL GREAT BASIN, THE NORTHERN PLAINS, THE TENNESSEE VALLEY, THE GREAT
LAKES, THE NORTHERN ROCKIES, THE SOUTHERN ROCKIES, THE MIDDLE MISSISSIPPI
VALLEY, THE NORTHEAST, THE NORTHERN GREAT BASIN, THE UPPER MISSISSIPPI VALLEY,
THE SOUTHEAST, THE CENTRAL APPALACHIANS, THE SOUTHERN PLAINS, THE OHIO VALLEY,
AND THE SOUTHWEST, SUN-FRI, DEC 24-DEC 29.

MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL
PLAINS, THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN
ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHEAST, THE SOUTHERN PLAINS, AND
THE OHIO VALLEY, MON-TUE, DEC 25-DEC 26.

MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT LAKES
AND THE UPPER MISSISSIPPI VALLEY, MON-WED, DEC 25-DEC 27.

SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF MAINLAND ALASKA,
SAT-WED, DEC 23-DEC 27.

MODERATE RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF MAINLAND
ALASKA, SAT-SUN, DEC 23-DEC 24.

SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER MISSISSIPPI
VALLEY, THE CENTRAL APPALACHIANS, THE TENNESSEE VALLEY, THE MID-ATLANTIC, THE
SOUTHERN APPALACHIANS, THE SOUTHEAST, THE SOUTHERN PLAINS, AND THE OHIO VALLEY,
SAT-SUN, DEC 23-DEC 24.

MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, AND THE TENNESSEE VALLEY, SAT-SUN, DEC 23-DEC 24.

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

DETAILED SUMMARY

FOR MONDAY DECEMBER 18 - FRIDAY DECEMBER 22: LOW PRESSURE OVER SOUTHEASTERN
CANADA SHOULD SUPPORT HIGH WINDS FROM THE GREAT LAKES TO THE NORTHEAST. WINDS
OVER THE GREAT LAKES COULD EXCEED 35 KNOTS, BEFORE THE THREAT SHIFTS EASTWARD,
WHERE WINDS OVER THE MOUNTAINS OF THE NORTHEAST ARE LIKELY TO EXCEED 50 MPH.



OVER THE SOUTHEAST, A LOW-PRESSURE SYSTEM IS FORECAST TO DEVELOP ALONG A
REMNANT FRONT. HEAVY RAINS (UP TO 2 INCHES IN 24 HOURS) ARE LIKELY DURING DEC
18-19, WITH A LOW THREAT OF ISOLATED SEVERE WEATHER. MODEL TIMING ON THE
PROGRESSION OF THE CONVECTION LIMITS PREDICTABILITY AT THIS TIME.



A LOW-PRESSURE SYSTEM MOVING INTO THE PACIFIC NORTHWEST IS LIKELY TO SPREAD
HEAVY PRECIPITATION AT LOWER ELEVATION WITH HEAVY SNOW AT HIGHER ELEVATION AND
FURTHER INLAND, DEC 18-19. THIS SYSTEM IS FORECAST TO MOVE ACROSS THE NORTHERN
ROCKIES AND REINTENSIFY OVER THE GREAT PLAINS. WARM ADVECTION SNOWS ARE LIKELY
OVER THE GREAT LAKES REGION LATER NEXT WEEK.



A PERIOD OF HIGH WINDS OVER SOUTHERN CALIFORNIA IS LIKELY LATER NEXT WEEK.
MODELS ARE SHOWING WIND SPEEDS OF AT LEAST 30 MPH, WHICH IMPLIES EVEN HIGHER
VALUES IN THE LOCATIONS WHERE TERRAIN FUNNELING CAN INCREASE WIND SPEEDS.



AN ACTIVE PATTERN IS FORECAST FOR SOUTHERN ALASKA, WITH HIGH WINDS (IN EXCESS
OF 45 MPH) FOR THE ALASKA PENINSULA AND THE ALEUTIANS, AND HIGH SIGNIFICANT
WAVE HEIGHTS (EXCEEDING 20 FEET) SURROUNDING THE ALEUTIANS DEC 18-19. ANOTHER
POTENTIAL PERIOD OF HIGH SIGNIFICANT WAVE HEIGHTS IS FORECAST ON DEC 20-21, BUT
UNCERTAINTY IS TOO HIGH TO DEPICT A HAZARD AT THIS TIME. INTERIOR ALASKA IS
LIKELY TO EXPERIENCE TEMPERATURES MUCH ABOVE NORMAL, FOR AN EXTENDED PERIOD OF
TIME. ANOTHER LOW-PRESSURE SYSTEM IS FORECAST TO MOVE NORTHWARD FROM THE GULF
OF ALASKA, AND BRING HEAVY PRECIPITATION (2 INCHES OF LIQUID EQUIVALENT IN 12
HOURS) TO PARTS OF ALASKA ON DEC 22. MODEL FORECASTS ARE UNCERTAIN ABOUT THE
SPECIFIC LOCATION (KENAI PENINSULA TO NORTHERN PANHANDLE), BUT BOTH THE GFS AND
ECMWF MODELS SHOW A POTENTIAL FOR A STORM SYSTEM.

FOR SATURDAY DECEMBER 23 - FRIDAY DECEMBER 29: WEEK-2 IS LIKELY TO FEATURE A
CONTINUATION OF THE WARMTH OVER ALASKA, THOUGH MUTED COMPARED TO THE RECENT
DAYS. THERE IS AT LEAST A 20 PERCENT CHANCE OF MAXIMUM TEMPERATURES BEING ABOVE
THE 85TH PERCENTILE DURING THE EARLY PORTION OF PERIOD, WITH ONLY A COUPLE OF
DAYS EXCEEDING A 40 PERCENT CHANCE OF EXCEEDING THE 85TH PERCENTILE.



OVER THE CONUS, A SLIGHT RISK (20-40 PERCENT CHANCE) OF MUCH BELOW NORMAL
MINIMUM TEMPERATURES IS FORECAST FROM THE ROCKIES TO THE GULF COAST AND
NORTHWARD TO THE GREAT LAKES AND NORTHEAST (DEC 24-29).  WITHIN THAT SLIGHT
RISK AREA, AN AREA OF A MODERATE RISK (40-60 PERCENT CHANCE) OF MUCH BELOW
NORMAL MINIMUM TEMPERATURES IS INDICATED OVER THE SOUTHERN PLAINS (DEC 25-26),
AND ANOTHER AREA OVER THE GREAT LAKES (DEC 25-27).



MODELS CONTINUE TO INDICATE THE THREAT FOR HEAVY PRECIPITATION OVER THE
TENNESSEE VALLEY DURING THE EARLY PORTIONS OF WEEK-2. TODAY, WITH SOME MORE
SPECIFICITY, MODELS ARE ALSO INDICATING THE POTENTIAL FOR LOW-LEVEL COLD AIR TO
INTERACT WITH THE PRECIPITATION, LEADING TO THE INTRODUCTION OF A FROZEN
PRECIPITATION HAZARD OVER THE TENNESSEE VALLEY AND SOUTHERN APPALACHIANS.
ADDITIONALLY, THE PATTERN IS LIKELY TO SUPPORT MULTIPLE EVENTS WITH
OROGRAPHICALLY ENHANCED PRECIPITATION FROM MONTANA TO EASTERN COLORADO.  LATER
IN WEEK-2, DAYS 10-12, MOST MODELS INDICATE A TRANSLATION OF THE STORM ACTIVITY
FROM THE LOWER MISSISSIPPI VALLEY TO THE NORTHEAST, THOUGH THE IMPACTS AND
TIMING ARE TOO UNCERTAIN TO DEPICT A HAZARD AT THIS TIME.



THE U.S. DROUGHT MONITOR, UPDATED ON DEC 12, SHOWS AN INCREASE IN AREAS OF
EXCEPTIONAL DROUGHT (D2-D4) TO 6.49% FROM 5.99%. MOST OF THE NEWLY INDICATED
SEVERE DROUGHT WAS OVER THE SOUTHERN PLAINS.

FORECASTER: MATTHEW ROSENCRANS

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.