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000
FXUS63 KGRR 121922
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
322 PM EDT SUN MAY 12 2013

LATEST UPDATE...
SYNOPSIS/SHORT TERM/LONG TERM/FIREWEATHER/HYDRO/MARINE

.SYNOPSIS...
ISSUED AT 228 PM EDT SUN MAY 12 2013

AN AREA OF HIGH PRESSURE OVER THE CENTRAL PLAINS WILL BUILD EAST
TONIGHT INTO MICHIGAN. THIS FAIR WEATHER SYSTEM WILL BRING WITH IT
CLEARING SKIES AND COLD TEMPERATURES. A FREEZE IS LIKELY FOR MUCH
OF THE REGION.  THE HIGH PRESSURE SYSTEM MOVES EAST OF THE STATE
TUESDAY. A WARMING TREND WILL DEVELOP. AS MOISTURE INCREASES THE
WEATHER COULD TURN UNSETTLED.


&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 228 PM EDT SUN MAY 12 2013

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE LOW
TEMPERATURES TONIGHT.

THERE WAS SOME MODEL INDICATIONS THAT THE CLOUDS WOULD REMAIN OVER
THE REGION EARLY THIS EVENING...AND WINDS COULD START TO INCREASE
LATER TONIGHT. THIS WOULD ACT TO LIMIT THE FREEZE RISK. HOWEVER
SATELLITE IMAGERY SHOWS CLOUDS DECREASING RAPIDLY FROM THE WEST.
MUSKEGON WILL LIKELY SCATTER OUT BY 5 PM. WITH THE PRESSURE
GRADIENT DECREASING ALONG WITH CLEARING SKIES DURING THE MID
AFTERNOON TO EVENING HOURS A FAVORABLE SETUP FOR RAPIDLY FALLING
TEMPERATURES THIS EVENING WILL EXIST. WHILE WINDS MAY TRY TO
INCREASE LATER TONIGHT...MAINLY NORTH OF GRAND RAPIDS...SUSPECT
THIS WILL NOT BE THE CASE GIVEN THE VERY COLD AND RELATIVELY DENSE
AIRMASS NEAR THE GROUND. WILL MAINTAIN THE CURRENT LOW
TEMPERATURES...GENERALLY IN THE 25 TO 30 DEGREE RANGE.

ALSO KEEPING AN EYE ON THE PRECIPITATION POTENTIAL FOR MONDAY
NIGHT THROUGH TUESDAY NIGHT. WARM AIR ADVECTION AND WEAKNESS IN
THE STABILITY ARRIVES LATER MONDAY NIGHT. COULD BE SOME ELEVATED
SHOWERS LATER AT NIGHT INTO TUESDAY. THE ATMOSPHERE BECOMES MORE
UNSTABLE LATER TUESDAY INTO TUESDAY NIGHT AS A COLD FRONT
APPROACHES FROM THE WEST. FORECAST SOUNDING FROM THE NAM AND GFS
DO SHOW THE INSTABILITY...BUT THERE IS ALSO SHOWN TO BE A SIZEABLE
NEGATIVE AREA ON THE SOUNDING. NOT CONVINCED THE MODELS HAVE A
GOOD HANDLE ON THE SITUATION JUST YET AND A LOW LEVEL JET NOSES IN
DURING THE NIGHT...SO WILL HOLD ONTO THE POPS. HIGHEST POPS
GENERALLY NORTH.



.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 228 PM EDT SUN MAY 12 2013

MAIN CHANGES:
- RAISED POPS WEDNESDAY TO CARRY OVER TUESDAY NIGHT THUNDERSTORM
CHANCES
- LOWERED POPS WEDNESDAY NIGHT AND THURSDAY...MAINLY NORTH OF I-96
- RAISED POPS FRIDAY...ESPECIALLY SOUTH OF I-96

KEPT BEST OVERALL CHANCES FOR SHOWERS AND THUNDERSTORMS SATURDAY
NIGHT AND SUNDAY. DID NOT MAKE ANY SIGNIFICANT ADJUSTMENTS TO
TEMPERATURES.

CURRENT AMPLIFIED UPPER PATTERN WILL BE MUCH MORE ZONAL BY THE
BEGINNING OF THE PERIOD. BOTH ECMWF AND GFS AGREE ON AN UPPER
POTENTIAL VORTICITY MAXIMUM CROSSING ONTARIO TUESDAY NIGHT INTO
WEDNESDAY WITH AN ASSOCIATED UPPER JET MOVING ACROSS THE NORTHERN
GREAT LAKES. EXPECT CHANCES FOR SHOWERS AND THUNDERSTORMS TO PERSIST
AT LEAST INTO THE EARLY PART OF WEDNESDAY.

THERE IS BETTER AGREEMENT BETWEEN THE LATEST AVAILABLE RUNS
OF THE ECMWF AND GFS WITH KEEPING A STATIONARY FRONT AND THE BEST
FOCUS FOR PRECIPITATION SOUTH OF THE CWA WEDNESDAY NIGHT AND THURSDAY.

THE 05/00 AND 05/12 RUNS OF THE ECMWF LIFT THE FRONT NORTH INTO THE
CWFA FRIDAY AHEAD OF AN APPROACHING UPPER TROUGH OVER THE WESTERN
CONUS. WITH THIS FOCUS...HAVE RAISED POPS DURING THE DAY FRIDAY.
THE 05/12 RUN SUGGESTS THAT CHANCES FOR SHOWERS AND THUNDERSTORMS
COULD CONTINUE WELL INTO FRIDAY NIGHT.


&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 123 PM EDT SUN MAY 12 2013

NO SIGNIFICANT CHANGES TO THE FORECAST. LIGHT RAIN SHOWERS IN THE
VICINITY OF THE LAN TERMINAL HAVE SWEPT SOUTHEAST OUT OF THE AREA
AND NO FURTHER PRECIPITATION IS EXPECTED. ADVERTISED CIGS AROUND
3500 FT AGL TODAY IN THE TAFS...BUT WOULD NOT BE SURPRISED TO SEE
THEM LIFT TO AROUND 4500 FT AGL LATER THIS AFTERNOON. STILL EXPECT
A RAPID DECREASE IN WINDS AND CLOUD COVER AREA WIDE AFTER SUNSET.


&&

.MARINE...
ISSUED AT 228 PM EDT SUN MAY 12 2013

WAVES OVER 5 FEET STILL ONGOING IN THE NEARSHORE AREA WILL KEEP
THE SMALL CRAFT ADVISORY GOING FOR THIS EVENING. WINDS AND WAVES WILL
GRADUALLY DIMINISH THROUGH THE NIGHT AS THE PRESSURE GRADIENT
WEAKENS. HIGH PRESSURE MOVES IN FOR MONDAY...SO NO HAZARDS
EXPECTED.

&&

.FIRE WEATHER...
ISSUED AT 228 PM EDT SUN MAY 12 2013

A DECENT AMOUNT OF SUN FOR MONDAY COUPLED WITH A DRY AIRMASS IN
PLACE WILL LOWER SURFACE HUMIDITY VALUES DURING THE DAY...LIKELY
UNDER 40 PERCENT. WESTERLY FLOW WILL DOMINATE THE DAY. GIVEN THE
WEAKER PRESSURE GRADIENT...WINDS WILL BE LIGHTER ON MONDAY THAN
THEY WERE TODAY.

&&

.HYDROLOGY...
ISSUED AT 228 PM EDT SUN MAY 12 2013

QPF AMOUNTS THROUGH WEDNESDAY EXPECTED TO BE LOW ENOUGH TO LIMIT
THE RISK FOR RISING WATER LEVELS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...FREEZE WARNING FROM 10 PM THIS EVENING TO 8 AM EDT MONDAY FOR
     MIZ037>040-043>046-050>052-056>059-064>067-071>074.

LM...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...MJS
HYDROLOGY...MJS
MARINE...MJS