Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 171140
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
640 AM CDT FRI APR 17 2015

.SHORT TERM /TODAY/...
ISSUED AT 403 AM CDT FRI APR 17 2015

FORECAST CONCERNS FOR TODAY WILL AGAIN REVOLVE AROUND TEMPERATURES
AND PRECIPITATION TRENDS. SOMEWHAT SIMILAR SET UP TO YESTERDAY AS
IOWA REMAINS IN AREA OF WEAK FLOW WITH LARGE UPPER LEVEL LOW
PRESSURE SYSTEM IN FOUR CORNERS REGION EXPECTED TO BEGIN TO LIFT
NORTHEASTWARD LATE IN THE DAY. THIS WILL BEGIN TO SPREAD BETTER
MOISTURE AND FORCING INTO IOWA WITH INCREASING PRECIPITATION
CHANCES. MODELS ARE AGAIN BRINGING INCREASED INSTABILITY INTO
WESTERN AND SOUTHERN IOWA...WITH SOUTHERN IOWA NEARING 1000 J/KG
CAPE LATE IN THE AFTERNOON. HOWEVER...FORCING AND SHEAR ARE VERY
WEAK. IN ADDITION...MODELS CONTINUE TO INDICATE A VERY DRY LAYER
NEAR THE SURFACE WHICH WILL HELP TO CUT BACK ON PRECIPITATION
CHANCES. BEST CHANCES WILL BE IN THE LATE AFTERNOON...AND HAVE CUT
BACK ON POPS FOR THE DAY...ESPECIALLY IN THE CENTRAL AND EAST AND
HAVE KEPT WESTERN POPS CONFINED TO THE LATE AFTERNOON...THOUGH STILL
HAVE LOW CONFIDENCE. LATEST MODEL RUNS APPEAR TO SLOW PROGRESSION OF
UPPER LOW...AND MAY BE TOO AGGRESSIVE WITH POPS.

HAVE KEPT TEMPERATURES NEAR GOING. WILL SEE WARMER TEMPERATURES THAN
YESTERDAY WITH BETTER MIXING AND WARMER TEMPS ALOFT. HAVE THEREFORE
KEPT TEMPERATURES NEAR GOING. HOWEVER...EXPECT CLOUDS TO CONTINUE TO
KEEP TEMPERATURES BELOW GUIDANCE.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 403 AM CDT FRI APR 17 2015

THE UPPER LOW ACROSS NORTHERN NEW MEXICO THIS MORNING WILL LIFT
SLOWLY NORTHEAST INTO EASTERN COLORADO TONIGHT THEN TRANSITION
INTO AN OPEN WAVE AS IT MOVES INTO NEBRASKA AND KANSAS LATE
SATURDAY AND SATURDAY NIGHT. SEVERAL IMPULSES WILL BE EJECTING
NORTHEAST FROM THE SYSTEM DURING THIS PERIOD WITH PRECIPITATION
CHANCES INCREASING FROM SOUTHWEST TO NORTHEAST. MOISTURE ADVECTION
WILL BEGIN TONIGHT AND BE MAXIMIZED BY SATURDAY AFTERNOON WITH
PROFILES SATURATING AND PWATS REACHING 1-1.25 INCHES BY LATE
SATURDAY. VERY WELL MAY BE A BREAK IN THE PRECIPITATION BETWEEN
THE ACTIVITY TONIGHT AND ANOTHER ROUND ON SATURDAY AFTERNOON. THE
TIGHTENING PRESSURE GRADIENT BY SATURDAY WILL PROMOTE BREEZY
EASTERLY WINDS OVER AT LEAST THE NORTHEAST HALF OF THE AREA WHICH
WILL BRING A PUSH OF DRIER AIR TO THAT AREA. THE BEST CHANCES FOR
PRECIPITATION WILL BE LATE SATURDAY AND SATURDAY NIGHT WHEN THE
PRIMARY KINEMATICS LIFT THROUGH THE STATE. DESPITE HIGH
POPS...THERE WILL BE DRY PERIODS DURING THIS TIME BETWEEN THE
ACTIVITY. MODEST MUCAPES OF 500 J/KG OR LESS WILL BE IN PLACE
ALONG WITH LOW STATIC STABILITIES SUGGESTED DUE TO THE LOW THETA-E
DIFFERENCES BETWEEN THE TROPOPAUSE AND THE BOUNDARY LAYER WILL
PROMOTE THUNDERSTORM POTENTIAL ACROSS THE ENTIRE AREA THOUGH WILL
BE MOST PREVALENT OVER CENTRAL AND SOUTHERN IOWA. THE
PRECIPITATION CHANCES WILL CONTINUE ON SUNDAY THOUGH A COLD FRONT
WILL BE MOVING ACROSS THE STATE WITH DRIER AIR ARRIVING FROM THE
WEST.

A STRONG UPPER LEVEL SYSTEM WILL DROP INTO THE NORTHERN PLAINS ON
SATURDAY AND WILL BECOME A CLOSED UPPER LOW BY LATE SUNDAY. THIS
SYSTEM WILL LINGER OVER THE WESTERN GREAT LAKES THROUGH AT LEAST
TUESDAY AND KEEP IOWA IN DEEP CYCLONIC FLOW AND COOLER CONDITIONS.
EARLY NEXT WEEK WILL BE COOL BUT PROFILES STILL SUGGEST FAVORABLE
CONDITIONS FOR A WELL MIXED BOUNDARY LAYER ALONG WITH DRY DEW
POINTS THAT WILL HELP BOOST DAY TIME HIGHS A BIT. STILL HIGHS WILL
GENERALLY BE IN THE 50S NEXT WEEK AND MUCH COOLER THAN THE PAST
SEVERAL WEEKS.

&&

.AVIATION...17/12Z
ISSUED AT 635 AM CDT FRI APR 17 2015

CONDITIONS WILL REMAIN VFR THROUGH PERIOD WITH LIGHT AND VARIABLE
WINDS. LOW PRESSURE SYSTEM WILL BEGIN TO INFLUENCE THE AREA NEAR
06Z...WITH INCREASING CHANCES FOR SHRA AND TSRA AT
SITES...ESPECIALLY WESTERN SITES KDSM/KFOD. HAVE INCLUDED VCSH
NEAR 12Z. MAY SEE MVFR CEILINGS AND VISIBILITIES BEYOND 12Z AS
WELL WITH INCREASING LOW LEVEL MOISTURE AND SHRA.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...AWB
LONG TERM...DONAVON
AVIATION...AWB


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