Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 201741
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
141 PM EDT MON OCT 20 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 327 AM EDT MON OCT 20 2014

A CLIPPER SYSTEM MOVING THROUGH THE GREAT LAKES WILL BRING MOSTLY
CLOUDY SKIES AND SCATTERED SHOWERS INTO TUESDAY MORNING. THE SYSTEM MOVES
OUT BY TUESDAY NIGHT ALLOWING HIGH PRESSURE TO BUILD INTO THE AREA
THROUGH THE REST OF THE WEEK. THAT WILL ALLOW FOR AN EXTENDED
PERIOD MOSTLY CLEAR SKIES AND SLOWLY WARMING TEMPERATURES.

&&

.UPDATE...
ISSUED AT 1045 AM EDT MON OCT 20 2014

MODIFIED POPS TO REFLECT CURRENT RADAR TRENDS AS UPPER TROUGH
MOVES THROUGH. ALSO ADDED SOME DRIZZLE THIS AFTERNOON AS STRATOCU
PUSHES SOUTHWESTWARD ACROSS THE CWA. RH PROFILES SHOW SOME LIFT IN
THE CLOUD LAYER AND THIS SHOULD LEAD TO SOME LIGHT DRIZZLE.

UPDATE ISSUED AT 752 AM EDT MON OCT 20 2014

I ADDED ISOLATED THUNDERSTORMS TO OUR FORECAST NEAR AND SOUTH OF
INTERSTATE 94 FOR THIS MORNING INTO THIS AFTERNOON. THE LATEST RUN
OF THE RAP13 SHOWS VERTICAL TOTAL ARE AROUND 30C NEAR THE CONVECTION
CROSSING SOUTHERN LAKE MICHIGAN AT 735 AM THIS MORNING. OUR TOTAL
LIGHTNING TRACKER IS SHOWING A HIGH FREQUENCY OF IN- CLOUD
LIGHTING WITH THESE STORMS (6-10 PER MINUTES). RAP SOUNDING IN
FRONT OF THE CONVECTION (UPPER WAVE ) SHOW 300 TO 400 J/KG OF
CAPE. THE LATEST SPC SREF 3 HOUR THUNDERSTORM PROBABILITY SHOWS THE
PROBABILITY OF THUNDERSTORMS GOES ALONG WITH THIS IDEA TOO. SO ALL
OF THIS TELLS ME THE LINE OF SHOWERS WILL KEPT MOVING EAST ACROSS
OUR SOUTHERN CWA THIS MORNING.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 327 AM EDT MON OCT 20 2014

THE WARM ADVECTION PRECIPITATION IS ALMOST OUT OF THE AREA SO THAT
WILL NOT BE AN ISSUE FOR FORECAST TODAY. THE MAIN ISSUE FOR TODAY
IS THE OUTSIDE CHANCE OF THUNDERSTORM THIS AFTERNOON EAST OF
GRAND RAPIDS. ONCE THAT IS DONE WE DO GET INTO ANOTHER COLD POOL
OF AIR THAT TYPICALLY LEADS TO LAKE EFFECT SHOWER WHICH WOULD
OCCUR FROM THIS EVENING INTO EARLY TUESDAY MORNING.

WHAT BRINGS THE THREAT FOR THUNDERSTORMS OVER OUR SE CWA LATE THIS
MORNING INTO EARLY THIS AFTERNOON IS THE 850 THERMAL RIDGE IS
UNDER THE 500 MB COLD POOL. SO THAT RESULTS IN VERTICAL TOTALS
NEAR 28C. THE 850 MB LI FALLS TO NEAR -1C OVER THE I-69 AREA
DURING THE EARLY AFTERNOON WHILE THIS IS HAPPENING. WE ALSO HAVE
THE EXIT REGION OF THE UPPER JET COMING INTO PLAY AT THIS TIME TO
HELP THE CAUSE. HOWEVER I DID NOT GO FOR THIS BECAUSE WHEN I
ACTUALLY LOOKED AT MODEL SOUNDINGS (RAP AND NAM) THERE IS AN
INVERSION NEAR 850 MB THAT WILL HARD TO OVERCOME. EVEN IF THAT CAN
BE OVERCOME THE CAPE IS VERY NARROW. SO MY SPIN WAS TO GO WITH
CHANCE POP FOR SHOWERS AND CALL THAT GOOD.

THE NEXT ISSUE IS LAKE EFFECT SHOWERS ONCE WE GET INTO THE 850
COLD POOL OF AIR TONIGHT. FOR A SHORT TIME... 6 PM TILL
MIDNIGHT... WE HAVE A MOIST LAYER TO NEAR 10000 FT WITH NORTH
WINDS BELOW THE INVERSION. THAT SHOULD RESULT OF IN LAKE EFFECT
SHOWERS OVER THE LAKE (NORTH WINDS) AND MAYBE TOUCHING THE POINTS
AND EXTREME WESTERN ALLEGAN AND VAN BUREN COUNTIES. THAT DOES NOT
LAST LONG... WINDS BECOME NORTH NORTHEAST AFTER MIDNIGHT AND PUSH
THAT SHOWERS OFF SHORE. BY 8 AM TUESDAY THE UPPER JET PASSES OVER
AHEAD AN INVERSION HEIGHTS CRASH TO NEAR 4000 FT AGL. SO WHAT EVER
THREAT THERE IS FOR SHOWERS QUICKLY ENDS.

WITH THE UPPER JET TO OUR EAST AND SURFACE HIGH PRESSURE BUILDING
IN I EXPECT CLEARING SKIES TUESDAY AFTERNOON AND THUS ANOTHER
BELOW FREEZING NIGHT EARLY WEDNESDAY MORNING. HIGH PRESSURE WILL
BRING SUNNY SKIES AND LIGHT WINDS FOR WEDNESDAY DURING THE DAY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 327 AM EDT MON OCT 20 2014

HIGH PRESSURE WILL CONTINUE IN CONTROL OF THE WEATHER PATTERN
WEDNESDAY NIGHT AND THURSDAY AND BRING FAIR AND DRY WX. A CONSENSUS
OF LATEST MEDIUM RANGE GUIDANCE CONTINUES TO SUGGEST THAT A MID
LEVEL SHORTWAVE WILL MOVE THROUGH THURSDAY NIGHT. HOWEVER THIS
WEAKENING SYSTEM SHOULD COME THROUGH DRY.

DRY AND MILD WEATHER IS ANTICIPATED FRIDAY THROUGH SATURDAY WITH
PERSISTENT SOUTHWESTERLY FLOW WAA. A WEAK COLD FRONT WILL COME
THROUGH SATURDAY BUT THIS SYSTEM IS ALSO LACKING IN MOISTURE AND
SHOULD COME THROUGH DRY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 136 PM EDT MON OCT 20 2014

A COLD FRONT PUSHING SOUTHEAST THROUGH THE TAF SITES IN SOUTHWEST
LOWER MI WAS PRODUCING A FEW SHOWERS AND EVEN AN ISOLATED
THUNDERSTORM. IN ADDITION LOWER CLOUD BASES WERE NOTED WITH MANY
SITES UNDER 2K FEET. THIS FRONT WILL PUSH SOUTHEAST OF KJXN BY
20Z. A PATCH OF CLEARING WAS SEEN BEHIND THE FRONT AND GENERALLY
VFR CLOUDS WERE NOTED TOWARD KMKG AND KFFX. THIS SHOULD BE THE
PREVAILING CONDITIONS THIS AFTERNOON. AS WE GO INTO THE LATE
AFTERNOON AND EVENING HOURS...LOWER CLOUDS ARE EXPECTED TO ADVECT
DOWN FROM THE NORTH. THERE COULD BE SOME DRIZZLE AS WELL. MVFR
CLOUD BASES ARE EXPECTED...WITH A LOW RISK FOR IFR. NOT MUCH
CHANGES INTO TUESDAY MORNING WITH MVFR CLOUDS TO PREVAIL.

&&

.MARINE...
ISSUED AT 327 AM EDT MON OCT 20 2014

WITH THE CORE OF WINDS TO 40 KNOTS MOVING EAST OF THE AREA BY
SUNRISE... WINDS WILL DECREASE FOR A TIME TILL THE COLD AIR POOL
AT MID LEVEL MOVES IN BY EARLY AFTERNOON. THEN I WOULD EXPECT
NORTH WINDS OF 15 TO 25 KNOTS INTO EARLY WEDNESDAY. SO I WILL
CONTINUE THE SMALL CRAFT ADVISORY AS IS AND CALL THAT GOOD.


&&

.HYDROLOGY...
ISSUED AT 327 AM EDT MON OCT 20 2014

LITTLE IN THE WAY OF SIGNIFICANT RAINFALL IS EXPECTED THROUGH
THIS COMING WEEKEND (ECMWF AND GFS ) SO RIVER LEVELS SHOULD SLOWLY
FALL OVER TIME.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 8 AM EDT WEDNESDAY FOR LMZ844>849.

&&

$$

UPDATE...93
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...LAURENS
AVIATION...MJS
HYDROLOGY...WDM
MARINE...WDM






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