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000
FXUS63 KGRR 191132
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
732 AM EDT SUN MAY 19 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 AM EDT SUN MAY 19 2013

FAIR AND MILD WEATHER IS ANTICIPATED TODAY. THE WEATHER PATTERN WILL
BECOME UNSETTLED MONDAY THROUGH WEDNESDAY AS A LOW PRESSURE SYSTEM
OVER THE UPPER MIDWEST BRINGS SEVERAL ROUNDS OF SHOWERS AND
THUNDERSTORMS TO OUR REGION. MILD WEATHER WILL CONTINUE THROUGH
MIDWEEK BEFORE TEMPERATURES COOL TO NEAR NORMAL LATE IN THE WEEK.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY AFTERNOON)
ISSUED AT 330 AM EDT SUN MAY 19 2013

OUR PRIMARY SHORT TERM FCST CHALLENGE IS TO DETERMINE PROBABILITIES
FOR THUNDERSTORMS AND EVALUATE THE POTENTIAL FOR SVR WX MONDAY
THROUGH TUESDAY.

FAIR AND WARM WX WILL CONTINUE TODAY WITH MAX TEMPS RANGING FROM THE
UPPER 70S OVER OUR NORTHERN COUNTIES TO MIDDLE 80S NEAR TO SOUTH OF
I-96. MOST OF TONIGHT SHOULD BE DRY BUT THERE IS A SMALL CHANCE OF A
SHOWER OR STORM TOWARD DAYBREAK MONDAY.

STRONG TO SEVERE STORMS ARE POSSIBLE MONDAY AFTERNOON AND EVENING AS
A CONSENSUS OF LATEST SHORT RANGE GUIDANCE SHOWS POTENTIAL FOR
MODERATE TO STRONG INSTABILITY TO DEVELOP MONDAY AFTERNOON WITH SB
CAPE VALUES POTENTIALLY REACHING AT LEAST 3000 J/KG OVER OUR
SOUTHERN COUNTIES.

DEEP MOISTURE IS LACKING BUT SFC DEW POINTS SHOULD REACH WELL INTO
THE 60S MONDAY. FCST SOUNDINGS SHOW AN INVERTED V TYPE SOUNDING SO
WILL HAVE TO WATCH FOR DAMAGING WIND GUSTS IN ADDITION TO POTENTIAL
FOR LARGE HAIL. THUNDERSTORMS SHOULD CONTINUE MONDAY NIGHT WITH A
WARM FRONTAL BOUNDARY IN THE AREA AND LATEST 00Z ECMWF GUIDANCE
SHOWING POTENTIAL FOR AN MCS TO TRACK AND TRAIN EAST ALONG THE WARM
FRONTAL BOUNDARY OVERNIGHT.

MORE SHOWERS AND STORMS ARE ANTICIPATED TUESDAY ALTHOUGH THE THREAT
FOR SVR WX TUESDAY IS A BIT LOWER THAN MONDAY WITH A CONSENSUS OF
00Z SHORT RANGE GUIDANCE SHOWING LESS IN TERMS OF INSTABILITY AND
MORE CLOUD COVER.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 330 AM EDT SUN MAY 19 2013

LITTLE QUESTION WE WILL START THIS PERIOD OUT WITH AN ACTIVE WEATHER
PATTERN FEATURING SHOWERS AND THUNDERSTORMS INTO WEDNESDAY NIGHT.
THERE IS A SLIGHT RISK THAT SEVERE STORMS COULD STILL HAPPEN INTO
WEDNESDAY EVENING. HOWEVER AS THE MEMORIAL DAY WEEKEND APPROACHES
THE STORY TURNS AROUND AS CANADIAN HIGH PRESSURE BUILDS IN WHICH
THEN BRINGS COOL... DRY WEATHER THROUGH MOST OF THE WEEKEND.

THE MODELS ARE IN REASONABLY GOOD AGREEMENT WITH THE OVERALL PATTERN
BUT THE ECMWF IS MORE AMBITIOUS WITH PHASING THE NORTHERN AND
SOUTHERN STREAM LATE IN THE WEEK. THAT MEANS COLD AIR INVADES THE
AREA IN THE FRIDAY TO SATURDAY TIME FRAME. ENOUGH SO THAT FROST MAY
BE POSSIBLE FRIDAY NIGHT AND SATURDAY NIGHT OVER NORTHERN AREAS.

THE LARGE SCALE UPPER AIR PATTEN FEATURES NUMEROUS CLOSED UPPER LOWS
AT MID LATITUDES ACROSS THE ENTIRE NORTHERN HEMISPHERE. OF INTEREST
TO SOUTHWEST MICHIGAN IS THE CLOSED UPPER LOW OVER THE CENTRAL AND
NORTHERN PLAINS (REX BLOCKED BY A CLOSED UPPER HIGH OVER ALBERTA AND
WESTERN ONTARIO) AND DEEPER CLOSED LOW IN THE GULF OF ALASKA. AS IT
TURNS OUT THE GULF OF ALASKA LOW SENDS SOME ENERGY OVER THE TOP OF
THE UPPER HIGH... RETROGRADING IT THEN ALLOWING IT TO GET ABSORBED
BY THE SUBTROPICAL HIGH OVER SOUTHERN TEXAS BY FRIDAY. MEANWHILE THE
SHORTWAVE THAT HEADS EAST OVER CENTRAL CANADA MERGES WITH SYSTEM
OVER EASTERN CANADA BY THEN. IT THEN STRONGLY DIGGING AN EASTERN
TROUGH BY LATE FRIDAY INTO EARLY SATURDAY. AS ALL OF THAT IS
HAPPENING THE CLOSED LOW OVER THE PLAINS GETS SHEARED OUT AND
ABSORBED BY THE DIGGING NORTHERN STREAM EASTERN CANADA TROUGH.
SOUTHWEST MICHIGAN END UP BETWEEN THE UPPER RIDGE TO OUR WEST AND
THE DEEP TROUGH TO OUR EAST. THAT IS A SET UP FOR COOL DRY WEATHER
HERE.

WHAT ALL OF THIS DOES IS CONTINUE THE THREAT OF SHOWERS AND
THUNDERSTORMS WITH THE FRONT STALLED NEAR SOUTHERN MICHIGAN INTO
WEDNESDAY AFTERNOON. THE LOW LEVEL JET IS AIMED AT SOUTHERN MICHIGAN
TUESDAY NIGHT INTO WEDNESDAY THEN REDEVELOPS OVER WESTERN INDIANA
WEDNESDAY AFTERNOON AS THE UPPER LOW STARTS TO SHEAR OUT. BY 8 PM
WEDNESDAY THERE IS A 35 TO 40 KNOT LOW LEVEL JET AIMED AT SOUTHEAST
MICHIGAN. GIVEN THE PRECIPITABLE WATER IS NEARLY DOUBLE NORMAL (NEAR
1.5 INCHES BY THEN) AND WE HAVE DEEP SOUTHERLY FLOW BEING LIFTED
OVER A STATIONARY FRONT BETWEEN I-94 AND I-96... I AM THINKING WE
WILL HAVE A CONSIDERABLE AMOUNT OF LAYERED CLOUDS AND SHOWERS
AROUND. THAT MAY DECREASE THE THREAT OF SURFACE BASED CONVECTION.
STILL IT WILL HAVE TO BE WATCHED. MUCAPES ARE STILL OVER 1000 J/KG
ON THE GFS WEDNESDAY AFTERNOON. ADD TO THE THE JET ENTRANCE REGION
LIFT AND SEEMS WE HAVE DECENT SET UP FOR SEVERE STORMS. WE WILL HAVE
TO WATCH THIS FOR SURE. THIS COULD BE THE BEST SET UP FOR SEVERE
STORMS OF THE WEEK FOR SOUTHWEST MICHIGAN.

FINALLY THE DIGGING NORTHERN STREAM TROUGH OVER EASTERN CANADA WILL
TAKE OVER AND CLEAR ALL THIS OUT TO OUR EAST. SO THURSDAY SHOULD BE
TRANSITIONAL. THE CANADIAN HIGH MOVES IN FRIDAY INTO SATURDAY SO
CLEAR SKIES...WINDS WILL BE LIGHT AND COOLER TEMPERATURES WILL
PREVAIL. HENCE THE RISK OF FROST UP NORTH FRIDAY NIGHT AND SATURDAY
NIGHT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 732 AM EDT SUN MAY 19 2013

SKIES START OFF NEARLY CLEAR THIS MORNING AND FOR THE MOST PART I
EXPECT MOSTLY CLEAR SKIES INTO THIS EVENING. A LAKE BREEZE IS
EXPECTED TO DEVELOP BY EARLY AFTERNOON SO I BROUGHT MKG`S WIND TO
THE SOUTHWEST THIS AFTERNOON. SOUNDINGS SEEM TO DRY FOR MUCH MORE
THAN A FEW CUMULUS CLOUDS TO DEVELOP. ALONG THE LAKE BREEZE
CONVERGENCE LINE CLOUDS MAY GO BROKEN FOR A SHORT WHILE BUT NOT
ENOUGH TO INCLUDE IN ANY TAFS.

TONIGHT AS THE WARM FRONT PUSHES NORTH DEW POINTS START TO PUSH UP
SO THAT MAY LEAD TO SOME SORT OF ADVECTION FOG SITUATION. I DO NOT
AT THIS POINT BELIEVE EXTENSIVE FOG SHOULD DEVELOP BUT MVFR VSBY
IS SURELY POSSIBLE. ALSO LATE TONIGHT THUNDERSTORMS MAY REACH AS
FAR AS MUSKEGON BEFORE DISSIPATING AS A WEAK LOW LEVEL JET TRIES TO
REACH SOUTHWEST MICHIGAN BUT WEAKENS BEFORE GETTING HERE.

&&

.MARINE...
ISSUED AT 330 AM EDT SUN MAY 19 2013

MINIMAL WAVE ACTION IS ANTICIPATED TODAY AND MONDAY BUT SOME AREAS
OF FOG MAY DEVELOP AS A MORE HUMID AIRMASS MOVES IN OVER RELATIVELY
COLD LAKE MI WATERS. THUNDERSTORMS WILL POSE A HAZARD TO MARINERS
MONDAY THROUGH WEDNESDAY.


&&

.FIRE WEATHER...
ISSUED AT 330 AM EDT SUN MAY 19 2013

MILD AND DRY WEATHER WILL CONTINUE TODAY AND INCREASING MOISTURE
WILL CAUSE RELATIVE HUMIDITY VALUES TO BE HIGHER THAN YESTERDAY.
WIND SPEEDS AGAIN TODAY WILL BE FAIRLY LIGHT.

&&

.HYDROLOGY...
ISSUED AT 330 AM EDT SUN MAY 19 2013

SEVERAL ROUNDS OF RAIN AND THUNDERSTORMS ARE EXPECTED MONDAY THROUGH
WEDNESDAY. THE STRONGEST STORMS MAY CONTAIN LOCALLY HEAVY RAINFALL
BUT ON AVERAGE AROUND AN INCH TO TWO INCHES OF RAIN IS EXPECTED TO
FALL ACROSS MUCH OF OUR AREA FROM MONDAY THROUGH WEDNESDAY.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...WDM
AVIATION...WDM
FIRE WEATHER...LAURENS
HYDROLOGY...LAURENS
MARINE...LAURENS