FXUS63 KGRR 071545
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1045 AM EST MON DEC 7 2009
LATEST UPDATE...SYNOPSIS/SHORT TERM...
.SYNOPSIS...(1045 AM EST MON DEC 7 2009)
LOW PRESSURE WILL BRING SOME SNOW TODAY WITH SOME ISOLATED HEAVY
AMOUNTS ACROSS AREAS FROM MUSKEGON TO HART WHERE ACCUMULATIONS OVER
6 INCHES ARE EXPECTED. ELSEWHERE...ONLY AN INCH OR TWO OF SNOW IS
EXPECTED NORTH OF INTERSTATE 96...AS THE LOW MOVES EAST.
A POWERFUL WINTER STORM WILL MOVE INTO THE SOUTHERN PLAINS STATES
TUESDAY AND THEN NORTHEAST INTO OUR AREA LATE TUESDAY NIGHT AND
WEDNESDAY. THIS STORM WILL BRING HEAVY SNOW NORTH OF INTERSTATE 96
TUESDAY NIGHT AND MIXED PRECIPITATION NEAR AND SOUTH OF INTERSTATE
96 RESULTING IN POTENTIALLY VERY HAZARDOUS TRAVEL CONDITIONS.
MIXED RAIN... FREEZING RAIN AND SNOW WEDNESDAY MORNING WILL QUICKLY
CHANGE TO WIND DRIVEN SNOW SHOWERS WEDNESDAY AFTERNOON AS IT TURNS
VERY WINDY AND SHARPLY COLDER ON THE BACK SIDE OF THE INTENSIFYING
LOW. HIGH WINDS... SNOW SHOWERS AND BLOWING SNOW WILL ADVERSELY
IMPACT TRAVEL WEDNESDAY AFTERNOON THROUGH THURSDAY. LAKE EFFECT SNOW
WILL CONTINUE THURSDAY NIGHT AND FRIDAY.
&&
.SHORT TERM...(1045 AM EST MON DEC 7 2009)
(TODAY THROUGH WEDNESDAY NIGHT)
ISSUED A WINTER STORM WARNING FOR MUSKEGON AND OCEANA COUNTIES WHERE
4 TO 6 INCHES OF SNOW HAD FALLEN IN A SMALL AREA OF STRONG SFC
CONVERGENCE ENHANCED BY LAKE MOISTURE BETWEEN 12Z AND 15Z THIS
MORNING. THIS SNOW WILL WEAKEN AS THE LOW MOVES EAST AND SFC
CONVERGENCE WEAKENS LEAVING BEHIND AMOUNTS OF 4 TO 7 INCHES IN AN
AREA FROM MUSKEGON TO HESPERIA. ALSO BUMPED UP POPS ACROSS THE
NORTHERN AND ESPECIALLY NORTHWEST FORECAST AREA FOR TODAY. REST OF
PREVIOUS FORECAST DISCUSSION FOLLOWS.
NUMEROUS SHORT TERM FCST CHALLENGES INCLUDE TIMING SNOW INTO OUR
CWFA LATE TUESDAY AND ALSO DETERMINING HOW MUCH SNOW WILL FALL FROM
LATE TUESDAY THROUGH WEDNESDAY NIGHT. WE ALSO NEED TO ADDRESS PCPN
TYPE ISSUES FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING.
A POWERFUL WINTER STORM OVER THE SOUTHERN PLAINS STATES TUESDAY WILL
INTENSIFY TO AROUND 980 MB NEAR GARY INDIANA BY 12Z WED AND THEN
DOWN TO AROUND 972 MB OVER GEORGIAN BAY BY WEDNESDAY EVENING. THIS
HAS POTENTIAL TO BE A HIGH IMPACT WINTER STORM FOR MUCH OF OUR CWFA.
WE ARE GOING WITH A BLEND OF 00Z ECMWF/GFS AS MODELS OF CHOICE SINCE
THEY ARE QUITE SIMILAR AND HAVE BEST CONTINUITY IN HOW THEY HANDLE
THE EVOLUTION OF THIS SYSTEM AND ARE ALSO THE PREFERRED MODELS OF
CHOICE BY HPC.
IMPACTS FROM THIS STORM WILL BEGIN TUESDAY EVENING AS WARM AIR
ADVECTION SNOW OVERSPREADS OUR CWFA AND INCREASES IN COVERAGE AND
INTENSITY NEAR AND NORTH OF I-96. I AM MOST CONCERNED ABOUT OUR NW
CWFA FOR HIGHEST END SNOW ACCUMULATIONS TUESDAY NIGHT. 00Z GFS
GUIDANCE ALSO SHOWS THAT RATHER STRONG MID LEVEL FGEN WILL DEVELOP
ACROSS THAT AREA FROM 06Z WED THROUGH 18Z WED.
HOWEVER EVEN OUR CENTRAL CWFA COULD SEE AT LEAST 3 TO 6 INCHES OF
SNOW TUESDAY NIGHT AS LOW LEVEL TEMPS WILL BE SLOW TO CREEP UP GIVEN
THE BRISK EASTERLY FLOW. EVENTUALLY ENOUGH WARM AIR WILL MORE THAN
LIKELY ADVECT INTO THE LOW LEVELS TO CAUSE MIXED RAIN... SNOW AND
POSSIBLY SOME FREEZING RAIN TO DEVELOP. SREF PROBABILISTIC AS WELL
AS SOME OF OUR NUMERICAL GUIDANCE IS SUGGESTING POTENTIAL FOR A FEW
HRS OF FZRA NEAR AND SOUTH OF I-96.
THE LEAST AMOUNT OF SNOW TUESDAY NIGHT IS EXPECTED ALONG THE I-94
CORRIDOR... WHERE ONLY AROUND AN INCH OR LESS OF SNOW SHOULD FALL
BEFORE PCPN BECOMES MIXED WITH OR CHANGES TO FZRA AND THEN RAIN.
OBVIOUSLY CHANGES TO THE EXPECTED LOW TRACK WOULD HAVE HUGE
IMPLICATIONS ON SNOW AMOUNTS AND PCPN TYPE ISSUES... SO WE WILL NEED
TO MONITOR SHORT RANGE GUIDANCE TRENDS REGARDING THIS SYSTEM VERY
CLOSELY.
A WINTRY MIX OF RAIN... SNOW AND POSSIBLY SLEET OR FREEZING RAIN
ACROSS MUCH OF OUR CWFA WEDNESDAY MORNING WILL QUICKLY CHANGEOVER TO
SNOW SHOWERS WEDNESDAY AFTERNOON. THIS WILL OCCUR AS VERY STRONG
WINDS DEVELOP ON THE BACK SIDE OF THE INTENSIFYING SFC LOW ADVECTING
MUCH COLDER AIR IN. IN FACT I AM CONCERNED ABOUT POTENTIAL FOR A
FLASH FREEZE TO OCCUR LATE WEDNESDAY AFTERNOON AND EVENING AS SFC
TEMPS PLUMMET INTO THE 20S RESULTING IN POTENTIALLY VERY HAZARDOUS
TRAVEL CONDITIONS.
WIND WHIPPED LAKE EFFECT SNOW SHOWERS ARE ANTICIPATED WEDNESDAY
NIGHT WITH POTENTIAL FOR AT LEAST ONE TO THREE INCHES OF ADDITIONAL
SNOWFALL AS SUGGESTED BY LATEST SREF GUIDANCE 12 HR MEAN SNOW PROGS
FROM 00Z THUR TO 12Z THUR. SNOW SHOWERS AND BLOWING SNOW AND HIGH
WINDS WILL CONTINUE TO CREATE POOR TRAVEL CONDITIONS WITH NEAR
BLIZZARD CONDITIONS AT TIMES POSSIBLE.
AS FOR TODAY... THE WEAK LOW PRESSURE SYSTEM WILL BRING LIGHT SNOW
WITH AROUND AN INCH OR TWO OF ACCUMULATION... MAINLY NEAR AND NORTH
OF A LINE FROM MKG TO MOP. MOST OF OUR GUIDANCE POPS ARE QUITE LOW
FOR OUR CENTRAL AND SOUTHERN CWFA TODAY. HOWEVER RGNL RADAR TRENDS
CONTINUE TO SHOW THAT SNOW CONTINUES TO DEVELOP ACROSS MUCH OF
NORTHERN ILLINOIS AND SOUTHERN LAKE MI. THEREFORE WE RAISED POPS TO
HIGH CHC FOR OUR CENTRAL AND SOUTHERN CWFA TODAY AND KEPT LIKELY
POPS GOING FURTHER NORTH.
&&
.LONG TERM...(410 AM EST MON DEC 7 2009)
(THURSDAY THROUGH SUNDAY)
LITTLE QUESTION THERE WILL BE A DEEP STORM DEPARTING THE AREA
THURSDAY INTO FRIDAY MORNING. THERE IS GOOD MODEL AGREEMENT INTO
THIS COMING WEEKEND TOO. THIS OF COURSE MEANS HIGHER THAN USUAL
FORECASTER CONFIDENCE.
WITH 850 MB TEMPERATURES NEAR -20C (SEEMS EACH NEW MODEL RUN GETS
COLDER WITH THIS FEATURE)...THE DGZ CLOSE TO THE GROUND AND THE MEAN
RH IN THE LOWER 5000 FT OVER 90 PCT... IT MAKES SENSE TO ME SNOW
SHOWERS WILL CONTINUE THROUGH FRIDAY. IN FACT AT 18Z FRI THE 1000 TO
700 MB RH ON THE GFS IS OVER 90 PCT OVER THE WESTERN 1/3 OF THE CWA.
BOUNDARY LAYER WINDS ARE IN THE 30 TO 40 KNOT RANGE THURSDAY AND 25
TO 35 KNOTS INTO FRIDAY MORNING. THIS MEANS SNOW FLAKES WILL BE
SMALL AND BLOWN A CONSIDERABLE DISTANCE DOWN WIND. IT ALSO MEANS
VISIBILITIES IN THE SNOW SHOWERS WILL BE LOWER THAN SNOW SHOWERS
WITH LARGE FLAKES DUE TO OPTICAL SCATTERING EFFECTS. WE COULD SEE
NEAR BLIZZARD CONDITIONS OVER A SIGNIFICANT AMOUNT OF THE CWA INTO
THURSDAY AFTERNOON (NORTH OF I-94). SO WHILE THE INVERSION HEIGHTS
ARE NOT ALL THAT HIGH AND THE UPPER LEVEL SHEAR ZONE WILL BE NORTH
OF THE GRR CWA... I STILL FEEL STRONGLY THERE WILL BE SNOW SHOWERS
ACROSS THE ENTIRE CWA. ACCUMULATIONS WILL NOT BE LARGE DUE TO THE
STRONG WINDS AND SMALL FLAKES. EVEN SO...THE WEATHER OUTSIDE WILL
NOT BE FRIENDLY FOR TRAVEL DUE TO LOW VISIBILITIES... TEMPERATURES
IN THE 15 TO 20 DEGREE RANGE AND WIND CHILLS NEAR ZERO. I BELIEVE
WE WILL STILL SEE SIGNIFICANT STORM IMPACTS ACROSS ALL BUT I-94 AND
SOUTH AREAS OF THE CWA INTO THURSDAY EVENING.
NEAR AND SOUTH OF INTERSTATE 94 THE WEST WINDS WILL PRECLUDE MUCH
LAKE EFFECT DUE TO SHORT OF RESIDENCE TIME OVER LAKE MICHIGAN FOR
THURSDAY INTO FRIDAY.
THE GFS CONTINUES TO SHOW STRONG SURFACE CONVERGENCE FROM US-131 TO
THE LAKE SHORE INTO SATURDAY AND THE 1000 TO 850 MB RH (WHICH IS IN
THE DGZ) WILL BE OVER 90 PCT DURING THAT ENTIRE TIME. SO I SEE NO
REASON TO BELIEVE THE SNOW SHOWERS WILL NOT CONTINUE. ALSO IN THE
FRIDAY NIGHT/SATURDAY TIME FRAME ANOTHER PUSH OF COLD AIR WITH AN
DECENT SHORTWAVE ROTATES THOUGHT THE GREAT LAKES. THUS MORE
CONVERGENCE AND LIFT FOR ADDITIONAL SNOW SHOWERS. SO I INCREASED POP
INTO THE WEEKEND.
I LOWERED TEMPERATURES ACROSS THROUGH MOST TIME PERIODS AS THE MODEL
TRENDS ARE FOR COLDER TEMPERATURES. THIS TREND IT TYPICAL WITH THE
POLAR VORTEX FORECAST TO DROP AS FAR SOUTH AS IT IS FORECAST TO COME
LATER THIS WEEK.
&&
.AVIATION...(635 AM EST MON DEC 7 2009)
AN AREA OF LIGHT SNOW IS FOR THE MOST PART EXPECTED TO STAY JUST
NORTH OF THE TAF SITES THIS MORNING AND EARLY THIS AFTERNOON. KMKG
WILL BE MOST IMPACTED BY THAT AREA OF SNOW WITH MVFR CIGS/VSBY AND
POSSIBLY IFR CIGS/VSBY AT TIMES AS THE SNOW AREA MOVES THROUGH. ALL
TAF SITES COULD BRIEFLY SEE SOME MVFR CIGS/VSBY AT TIMES THIS
MORNING FROM THE SNOW BEFORE DRIER AIR IMPROVES CONDITIONS TO VFR BY
LATE AFTERNOON AT ALL TAF SITES.
&&
.MARINE...(410 AM EST MON DEC 7 2009)
A GALE WATCH HAS ALREADY BEEN ISSUED AND REMAINS IN EFFECT FROM
WEDNESDAY AFTERNOON THROUGH THURSDAY EVENING. HIGH END GALES ARE
ANTICIPATED IN THIS TIME FRAME. IN FACT I AM BECOMING INCREASINGLY
CONCERNED ABOUT POTENTIAL FOR STORM FORCE WINDS.
&&
.HYDROLOGY...(410 AM EST MON DEC 7 2009)
NO HYDRO ISSUES THROUGH TUESDAY AFTERNOON. PRIMARILY SNOW IS
ANTICIPATED ACROSS OUR NORTHERN AND CENTRAL HSA TUESDAY NIGHT WITH
MIXED RAIN AND SNOW DEVELOPING ACROSS OUR SOUTHERN HSA. MIXED PCPN
WEDNESDAY MORNING WILL QUICKLY CHANGEOVER TO SNOW SHOWERS WEDNESDAY
AFTERNOON AS IT TURNS VERY WINDY AND SHARPLY COLDER ON THE BACK SIDE
OF THE INTENSE LOW. PLUMMETING TEMPERATURES INTO THE TEENS WEDNESDAY
NIGHT THROUGH THURSDAY WILL MITIGATE POTENTIAL FOR ANY SIGNIFICANT
HYDRO ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING FOR MUSKEGON AND OCEANA COUNTIES THROUGH 3
PM FOR MUSKEGON AND OCEANA COUNTIES.
WINTER STORM WATCH FOR ENTIRE CWFA WITH THE EXCEPTION OF CALHOUN AND
JACKSON COUNTIES FROM TUESDAY EVENING THROUGH WEDNESDAY NIGHT.
LM...GALE WATCH ST. JOSEPH TO MANISTEE FROM WEDNESDAY AFTERNOON
THROUGH THURSDAY EVENING.
&&
$$
SYNOPSIS: OSTUNO/LAURENS
SHORT TERM: OSTUNO/LAURENS
LONG TERM: WDM
AVIATION: WDM
MARINE: LAURENS
HYDROLOGY: LAURENS
