Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 122048 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 348 PM EST FRI FEB 12 2016 .SYNOPSIS... AN ARCTIC COLD FRONT WILL CROSS THE REGION TONIGHT THROUGH SATURDAY USHERING IN THE COLDEST AIRMASS OF THE SEASON THUS FAR. AS THIS COLD AIR INTERACTS WITH A TROUGH OF LOW PRESSURE OVER THE GULF OF MAINE...A PERIOD OF MODERATE TO HEAVY SNOW WILL BE POSSIBLE ALONG THE MIDCOAST REGION OF MAINE. BEYOND THIS...THE COMBINATION OF COLD TEMPERATURES AND STRONG NORTHWEST WINDS WILL CAUSE DANGEROUSLY COLD WIND CHILLS SATURDAY NIGHT AND SUNDAY. TEMPERATURES WILL RAPIDLY MODERATE NEXT WEEK WITH A WINTRY MIX OF PRECIPITATION POTENTIALLY TRANSITIONING TO RAIN ON MONDAY NIGHT AND TUESDAY ALONG WITH STRONG SOUTHERLY WINDS. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... HIGH IMPACT WEATHER POTENTIAL: SNOW DEVELOPS ALONG THE MIDCOAST OVERNIGHT. CURRENT PATTERN: EARLY AFTERNOON WATER VAPOR IMAGERY REVEALS RIDGE- TROUGH PATTERN ACROSS THE CONUS...WITH IMPRESSIVE PORTION OF THE POLAR VORTEX CURRENTLY CENTERED OVER JAMES BAY. SOUTH OF THIS FEATURE...WATER VAPOR IMAGERY DEFINES A DIGGING SHORTWAVE /DARKENING OF THE IMAGERY/ OVER THE NORTHERN OHIO VALLEY. THIS WILL HELP FORCE CYCLOGENESIS OFF THE MID ATLANTIC COAST THAT WILL RACE NORTHEAST WELL SOUTH AND EAST OF NEW ENGLAND THROUGH SATURDAY. A WEAKER SURFACE LOW IS CURRENTLY DEPICTED OVER THE EASTERN GREAT LAKES ASSOCIATED WITH FORCING AHEAD OF THE H5 LOW OVER JAMES BAY. AS THIS LATTER FEATURE DIVES SOUTH AND EAST TOWARDS NEW ENGLAND THIS WEEKEND...THE ASSOCIATED SURFACE LOW WILL BE ABSORBED INTO THE DEVELOPING SYSTEM OFFSHORE. OUR PRIMARY WEATHER IMPACTS WILL BE 1- WHAT HAPPENS BETWEEN THESE SYSTEMS AS IMPRESSIVE MID AND UPPER LEVEL FORCING COMBINES WITH VERY SUBSTANTIAL INSTABILITY OVER THE RELATIVELY WARM GULF OF MAINE WATERS AND 2- THE RAMIFICATIONS OF ARRIVING ARCTIC AIR. TEMPS AT H8 THIS MORNING WERE -35C OVER JAMES BAY WITH TEMPERATURES CLOSE TO THIS REACHING NEW ENGLAND ON SATURDAY...PRESENTING WIND CHILL CONCERNS AS IMPRESSIVE COLD ADVECTION DRIVES THIS AIR INTO THE REGION. TONIGHT: EXPECT A GENERAL INCREASE IN MID AND UPPER LEVEL CLOUDINESS PER A LOOK AT AFTERNOON VISIBLE SATELLITE IMAGERY AS WEAK WARM ADVECTION CONTINUES AHEAD OF APPROACHING SURFACE LOW NOW NORTH OF LAKE ONTARIO. FORCING FOR ASCENT WILL BE ON THE INCREASE WITH TOP DOWN SATURATION LIKELY BRINGING SNOW SHOWER ACTIVITY INTO THE MOUNTAINS OVERNIGHT. WE/LL TALK MORE ABOUT THE NORLUN EVENT IN THE SHORT TERM SECTION BELOW...BUT EXPERIMENTAL HRRR IS ON BOARD WITH THE 12Z GUIDANCE SUITE IN DEVELOPING LLEVEL CONVERGENCE IN THE VICINITY OF PENOBSCOT BAY BY MIDNIGHT TONIGHT...WITH SNOW DEVELOPING IN THIS REGION AND CONTINUING THROUGH THE MORNING. WITH A GOOD FLUFF FACTOR HELPING ACCUMULATIONS...COULD SEE 1-3 INCHES OVER KNOX/WALDO COUNTIES BY DAYBREAK. TEMPERATURES: WITH SOUTHWEST FLOW ONGOING AND CLOUDS ON THE INCREASE...TEMPERATURES WILL BE A GOOD BIT WARMER THAN THE PREVIOUS NIGHT BUT GIVEN THE CHILLY HIGHS OF TODAY...WILL CERTAINLY NOT BE WARM. EXPECT LOWS IN THE SINGLE DIGITS IN THE MOUNTAINS THROUGH THE LOWER TEENS ALONG THE COAST. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... ...SIGNIFICANT SNOW ALONG THE MID COAST BECOMING INCREASINGLY LIKELY SATURDAY... ...DANGEROUSLY COLD WIND CHILLS SATURDAY NIGHT THROUGHOUT THE REGION... HIGH IMPACT WEATHER POTENTIAL: HEAVY SNOW TOTALS POSSIBLE IN THE VICINITY OF PENOBSCOT BAY SATURDAY WITH ATTENTION THEN TURNING TO ADVISORY-WARNING LEVEL WIND CHILLS SATURDAY NIGHT. SATURDAY: CORE OF H5 LOW ALOFT SINKS FROM JAMES BAY AT DAYBREAK SOUTH AND EAST INTO NORTHERN NEW ENGLAND TOWARDS EVENING WITH T8S NEARING -30C OVER MY WESTERN ZONES BY 00Z/SUN. COL REGION BETWEEN LOW LEVEL REFLECTION OF THIS H5 LOW AND THE DEVELOPING SYSTEM WELL SOUTH AND EAST OF THE BENCHMARK APPEARS TO BE ALLOWING ALL THE INGREDIENTS FOR A BONA-FIDE NORLUN EVENT TO BE PRESENT AS THE H8 FLOW GOES SLACK ALONG WITH A DEVELOPING LLEVEL CONVERGENCE ZONE. THERE WILL BE AMPLE INSTABILITY IN THE LLEVELS WITH WATER SURFACE TO H8 DELTA TS NEAR -15 AND DELTA TS TO H7 NEARING -30C. THIS ALLOWS FOR A TREMENDOUS AMOUNT OF LLEVEL INSTABILITY...WITH OCEAN-INDUCED CAPE VALUES OF 500-1000 J/KG PORTRAYED ON THE 12Z NAM AND GFS. THIS COULD VERY WELL PROMOTE THUNDER WITH ANY SNOW BAND THAT DOES DEVELOP. SNOW RATIOS: THE DENDRITIC GROWTH ZONE WILL BE BELOW THE PRIMARY AREA OF LIFT DURING THE HEIGHT OF THE EVENT...BUT IT WILL STILL GET CLIPPED AND SEE NO REASON WHY WE CAN/T FORCE 15-20:1 RATIOS OUT OF THIS SETUP. THERE IS UNCANNY AGREEMENT IN THE 12Z SUITE /NAM-GFS-ECMWF-GEM/ ON THE PLACEMENT OF THE MESOSCALE BAND OVER PENOBSCOT BAY. WHILE THIS WOULD TEND TO SUGGEST ABOVE NORMAL CONFIDENCE...THE FACT THAT THIS IS A NORLUN EVENT BEGS CAUTION. A LOOK A THE 00Z NCAR ENSEMBLE SHOWS ABOUT 40% OF THE MEMBERS DIRECTLY IMPACTING OUR AREA. WOULD REALLY LIKE TO SEE THIS EVENT COME INTO THE NEAR TERM-HIGH RESOLUTION GUIDANCE WINDOW AND AS SUCH...WITH THE WORD OUT RIGHT NOW WITH THE WATCH...WILL LET THE EVENING SHIFT TAKE A FINAL LOOK AT THINGS BEFORE MAKING A FINAL DECISION ON WINTER STORM WARNINGS VS. WINTER WEATHER ADVISORIES. THAT BEING SAID...CERTAINLY CANNOT RULE OUT SOME 1 FOOT+ SNOWFALL AMOUNTS SOMEWHERE IN THE MID COAST REGION GIVEN THE SETUP ABOVE. TEMPERATURES: MAY RISE SLIGHTLY IN THE EARLY MORNING...BUT WILL THEN REVERSE COURSE AND FALL THROUGH THE AFTERNOON WITH ALL LOCATIONS IN THE SINGLE DIGITS ABOVE AND BELOW ZERO BY EVENING. WIND CHILLS WILL REACH ADVISORY LEVELS IN THE MOUNTAINS IN THE AFTERNOON...WITH THE MOST DANGEROUS VALUES HOLDING OFF UNTIL SATURDAY NIGHT. NONETHELESS...WIND CHILLS WILL BECOME INCREASINGLY DANGEROUS BY LATE AFTERNOON/EVENING. WINDS: VERY IMPRESSIVE COLD AIR ADVECTION WILL YIELD STEEP LLEVEL LAPSE RATES...WHICH SHOULD BE ABLE TO MIX ANYTHING THE ATMOSPHERE HAS TO OFFER WIND-WISE IN THE LOWEST 5KFT. HIGHEST WINDS IN THE COLUMN ARE AROUND 30KTS /A BIT HIGHER OFFSHORE/ SO WILL PAINT GUSTS AROUND 30MPH INLAND /HIGHER ON THE HILLTOPS/ AND 30-40MPH ALONG THE COAST. NOTE: WINDS WILL NOT BE THIS STRONG IN THE VICINITY OF THE NORLUN TROUGH AND THUS SIGNIFICANT BLOWING/DRIFTING WILL NOT INITIALLY BE A PROBLEM. HOWEVER...BY SATURDAY EVENING...THERE WILL LIKELY BE SIGNIFICANT BLOWING/DRIFTING...AND WILL HAVE TO WATCH FOR THIS IF THE SNOW DOES MATERIALIZE. SATURDAY NIGHT: H5 LOW OPENS UP AND SHIFTS EAST WITH THE CORE OF THE COLDEST AIR ALOFT OVERHEAD UNDER CONTINUED STRONG NORTHWEST WINDS AS GRADIENT BETWEEN 1035 MB HIGH OVER THE GREAT LAKES COMBINES WITH OFFSHORE-MOVING NORLUN TO CONTINUE WINDS OF 15G25KTS. CONCERNS WILL TURN TO DANGEROUSLY COLD WIND CHILLS...WHICH SHOULD HAVE NO PROBLEM HITTING WARNING CRITERIA IN THE MOUNTAINS AND FOOTHILLS...BUT LIKELY REMAIN AT ADVISORY LEVELS ALONG THE COAST. AM HONESTLY A BIT SURPRISED IN THE MET/MAV LOW TEMPERATURE SPREAD AS WE SHOULD REMAIN WELL-MIXED THROUGH THE NIGHT. DID GIVE SOME NOD TO THE COLDER MET...WITH LOWS BELOW ZERO IN ALL LOCATIONS...AND PERHAPS AS LOW AS -20 IN THE MOUNTAINS. && .LONG TERM /SUNDAY THROUGH FRIDAY/... HIGH IMPACT WEATHER: DANGEROUSLY COLD WIND CHILLS LINGER INTO AT LEAST SUNDAY MORNING. A STORM COULD BRING SNOW/FREEZING RAIN/RAIN TO THE REGION MONDAY NIGHT INTO TUESDAY NIGHT. STRONG WINDS ARE POSSIBLE WITH THIS SYSTEM AS WELL. DEEP PERSISTENT 500 TROUGH OVER THE ERN CONUS ON SUNDAY WILL SHIFT NE AND WEAKEN BY EARLY NEXT WEEK...AND THIS ALLOWS THE HEMISPHERIC WAVE PATTERN TO BECOME LESS AMPLIFIED WITH A HIGHER WAVE NUMBER. THE OVERALL +PNA PATTERN WEAKENS EARLY TO MID-WEEK...AND TRIES TO BREAK DOWN BY THE END OF THE WEEK. OF NOTE THOUGH...IS SRN STREAM WAVE THAT DIGS OVER S CENTRAL CONUS MON AND LIFTS NWD TUE AND WED AS NRN STREAM DIVES INTO IT AND THIS COULD PRODUCE THE HIGH IMPACT STORM OVER NEW ENGLAND AROUND TUESDAY. SUNDAY START IN THE THROES OF THE THE VERY COLD AIR MASS IN THE REGION WITH STRONG PRES GRAD IN PLACE AND GUSTY NW WINDS. THE DANGEROUS WIND CHILLS LINGER THRU THE MORNING BUT AS TEMPS WARM FROM LOWS BELOW ZERO EVERYWHERE...AND WITH PRES GRADIENT SLACKENING AS SFC HIGH BUILDS IN SHOULD SEE WIND CHILLS RISE TO MORE BEARABLE LVLS BY AFTERNOON. STILL...THE TAIL OF THE CAA WILL HOLD THRU MOST OF THE DAY AND HIGHS WILL STRUGGLE TO REACH ZERO IN THE N...AND TO REACH 10F IN THE SOUTH. AS THE SFC HIGH MOVES OVER THE REGION LOOK FOR DECOUPLING IN MOST PLACES AND VERY GIVEN GOOD RAD COOLING GIVEN COLD AIR IN PLACE AND A STARTING POINT NEAR OR BELOW ZERO. WENT BELOW SUPERBLEND FOR MINS IN MOST PLACES...AND SIGNIFICANTLY BELOW IN THE MORE SHELTERED SPOTS. THIS SHOULD BRINGUS LOWS 10 BELOW TO ZERO IN THE COASTAL PLAIN...WITH LOWS DROPPING TO -20 OR LOWER IN THE SHELTERED MOUNTAIN VALLEYS. ON MONDAY LOOK FOR WARMER AIR TO START WORKING IN...AND HIGHS REBOUND INTO THE TEENS TO MID 20S...WITH INCREASING CLOUDS IN THE AFTERNOON. THE NEXT SYSTEM MOVES IN ON MON NIGHT AND TUE. SOME DIFFERENCES IN THE MODEL AS TO HAVE FAR W THE SFC LOW TRACKS...WITH THE GFS AND GGEM PASSING IT S-N THRU THE MIDDLE OF ME...AND THE EURO AND GEFS MEAN BRINGING IT NWD ALONG THE NY/VT BORDER...WHICH WOULD BE THE WARMER SOLN...AND LIKELY LEAD TO SNOW TO FZRA/PL TO RAIN SOLN IN MANY SPOTS. THE MORE EASTERLY TRACK WOULD SEE SNOW LAST LONGER INTO THE STORM AWAY FROM THE COAST. P-TYPE WILL BE ONE OF THE BIG ISSUES WITH THIS SYSTEM AND CONFIDENCE IS LOW AS TO HOW IT WILL ALL UNFOLD. ONE THING TO NOTE IS THAT WE ARE COMING OUT OF VERY COLD AIRMASS...AND DESPITE THE BEST WINDS ABOVE THE INVERSION IT WILL BE SLOW TO BREAK OUT OF THAT LOW LVL COLD AIR...WHICH WILL PROBABLY HOLD ON LONGER THAN THE MODELS SUGGEST. ANOTHER ISSUE COULD BE STRONG WINDS...ALTHOUGH WITH THE INVERSION MAY BE TOUGH FOR THOSE WINDS TO MIX TO THE SFC...AT LEAST FOR ANY SIGNIFICANT LENGTH OF TIME. THE WHOLE SYSTEM WILL MOVE OUT LATE TUE NIGHT AND WED. COULD BUST OUT INTO WARMER AIR ON WED BEHIND THE SYSTEM WITH HIGHS CLIMBING INTO THE UPPER 30S TO LOW 40S. COLD FRONT SWINGS THRU WED NIGHT WITH UPPER LVL TROUGH ON THU AND TEMPS DROP BACK AGAIN...BELOW NORMAL...BUT NOT TOO FAR...WITH HIGHS IN THE 20S TO AROUND 30. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... SHORT TERM...VFR UNDER MOSTLY CLEAR CONDITIONS ATTM. EXPECT DETERIORATING CONDITIONS THROUGH THE COMING TAF PERIOD WITH SNOW DEVELOPING OVERNIGHT AT RKD AND LIKELY AUG WITH IFR/LIFR RESTRICTIONS. FOR A PERIOD SATURDAY...INCH PER HOUR SNOWFALL RATES ARE POSSIBLE...MOST LIKELY AT RKD. FURTHER WEST...ARCTIC FRONT WILL BRING A ROUND OF SNOW SHOWERS...MOST LIKELY TO BRING RESTRICTIONS TO LEB/HIE...BUT BRIEF RESTRICTIONS ARE POSSIBLE SOUTH AND EAST OF THIS AS WELL. CONDITIONS IMPROVE SATURDAY NIGHT WITH VFR CONDITIONS RETURNING FOR SUNDAY. AFTER LIGHT WINDS OVERNIGHT...STRONG NORTHWEST WINDS /15G25KTS/ WILL DEVELOP BY LATE MORNING SATURDAY AND CONTINUE THROUGH SATURDAY NIGHT. LONG TERM...MAINLY VFR SUN THRU MON WITH GUSTY NW WINDS DIMINISHING DURING SUN AFTERNOON. COULD SEE EXTENDED PERIOD OF IFR OR LOWER IN SN/FZRA/RA MON NIGHT INTO TUE NIGHT. && .MARINE... SHORT TERM...WINDS/WAVES BELOW SMALL CRAFT LEVELS INTO TOMORROW MORNING BEFORE INTENSE COLD ADVECTION BEHIND AN ARCTIC COLD FRONT BRINGS A PERIOD OF GALES TO THE OUTER WATERS BY LATE SATURDAY AFTERNOON THROUGH SUNDAY MORNING WITH WINDS LIKELY REMAINING BELOW GALE FORCE IN THE BAYS. IN ADDITION...HEAVY FREEZING SPRAY WARNINGS HAVE BEEN HOISTED SATURDAY EVENING THROUGH SUNDAY MORNING GIVEN THE COMBINATION OF THE AFOREMENTIONED WINDS AND THE COLDEST AIRMASS OF THE SEASON THUS FAR. LONG TERM...NW WIND DIMINISH SLOWLY THRU SUNDAY...AS DOES INTENSITY OF FREEZING SPRAY...BUT WILL LKLY HOLD TO SCA WINDS THRU SUN EVE. AFTER A BRIEF BREAK IN THE WINDS ON MON AND MON NIGHT...LOOK FOR S WINDS TO REACH SCA LVLS EARLY TUE AND COULD REACH GALES BY TUE AFTERNOON AND EVE...BEFORE DIMINISHING WED. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...WIND CHILL WARNING FROM MIDNIGHT SATURDAY NIGHT TO 10 AM EST SUNDAY FOR MEZ012>014-018>022. WIND CHILL WARNING FROM 7 PM SATURDAY TO 10 AM EST SUNDAY FOR MEZ007>009. WIND CHILL ADVISORY FROM MIDNIGHT SATURDAY NIGHT TO 10 AM EST SUNDAY FOR MEZ023>028. WINTER STORM WATCH FROM MIDNIGHT EST TONIGHT THROUGH SATURDAY EVENING FOR MEZ022-027-028. NH...WIND CHILL WARNING FROM MIDNIGHT SATURDAY NIGHT TO 10 AM EST SUNDAY FOR NHZ004>013-015. WIND CHILL WARNING FROM 7 PM SATURDAY TO 10 AM EST SUNDAY FOR NHZ001>003. WIND CHILL ADVISORY FROM MIDNIGHT SATURDAY NIGHT TO 10 AM EST SUNDAY FOR NHZ014. MARINE...HEAVY FREEZING SPRAY WARNING FROM 7 PM SATURDAY TO 10 AM EST SUNDAY FOR ANZ150>154. SMALL CRAFT ADVISORY FROM NOON SATURDAY TO 10 AM EST SUNDAY FOR ANZ151-153. GALE WARNING FROM 4 PM SATURDAY TO 10 AM EST SUNDAY FOR ANZ150- 152-154. && $$ SYNOPSIS...ARNOTT NEAR TERM...ARNOTT SHORT TERM...ARNOTT LONG TERM...CEMPA AVIATION...ARNOTT/CEMPA MARINE...ARNOTT/CEMPA

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