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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
331 am CDT Sat Jul 4 2015

issued at 330 am CDT Sat Jul 4 2015

The latest surface analysis was indicating ridge axis occupying much of
the Central Plains into the southwestern Great Lakes/including the
entire dvn County Warning Area which currently has calm winds/...with a weak trough
sagging across east central Minnesota...northwest WI and the u.P. Of Michigan. To
the west of the ridge...return flow was seen organizing across the
Western Plains. upper ridge lobe was pressing eastward
toward the upper MS River Valley...while further upstream a vorticity maximum
was seen on water vapor imagery across the Dakotas.


Short term...(today and tonight)
issued at 330 am CDT Sat Jul 4 2015

Today...patchy fog early...then the surface ridge overhead will slowly
migrate eastward enough to allow light return flow to take over as
the day progresses. The upstream upper ridge axis mentioned above
will continue to push east across the local area today maintaining
the fair weather regime into the evening. Somewhat moderating thermal
profiles and prognosticated mixing depth support model guidance
widespread lower 80s today...with a few locations pushing the middle
80s. Surface dewpoints in the upper 50s to lower 60s combined with the warm
ambient temperatures will keep a lid on the humidity levels. Another day
with advected smoke aloft making for hazy filtered sunshine.

Tonight...the elongated vorticity complex will look to push out of the
northern plains and across the upper MS River Valley into south central
Iowa by Sunday morning. But feel not enough low level moisture return and
convergence on it/S incoming vorticity gradient to fuel much of any
precipitation generation in or just to the west of the local forecast area and
will maintain a dry forecast. Light south to southeast surface flow to
continue... but there still may be some patchy fog or valley fog
with the chance for the surface winds to decouple from time to time. A
category milder low temperature regime as compared to previous nights with
the light return flow and lows in the upper 50s to lower 60s.

Long term...(sunday through next friday)
issued at 330 am CDT Sat Jul 4 2015

Main focus is on the frontal passage that will bring widespread rain
and thunderstorms Monday into Monday night. Ahead of this...warm
advection southerly flow will bring much warmer and considerably
more humid conditions for Sunday.

The combination of high pressure shifting into the eastern Great
Lakes and a developing Lee trough over the plains will lead to S-southeast
winds that will advect a more moist middle MS valley airmass northward
into the region. This should result in dewpoints rising into the middle
60s to near 70 for noticeably more humid conditions Sunday. Warming
aloft still supports highs in the middle 80s and possibly upper 80s.
Cloud cover will be increasing Sunday night as blowoff from upstream
mesoscale convective system activity overspreads the area...which combined with increasing
low level moisture will hold mins in the middle 60s to around 70.

Monday...the 00z GFS came in faster with the cold frontal
passage...while the NAM...European model (ecmwf) and Canadian were in better
consensus with a slower frontal passage which would not exit to the east until
well after midnight. Have trended toward the more reasonable slower
solutions...which delays and lowers probability of precipitation over the east...while
keeping likely to categorical probability of precipitation going west for afternoon into
evening...spreading east overnight. There is still a suggestion of
elevated convection popping up over the area in the morning...which
is handled with slight to low end chance probability of precipitation. Forecast precipitable water values
well over 2 inches may be overdone...and influenced by prognosticated
dewpoints shown in the middle 70s ahead of the front which seem too
high considering the lack of moisture pooling and deep mixing.
However...moisture levels will still be seasonably high...leading to
a threat of heavy rain. MUCAPES values at least into the 1500 to
2000 j/kg range with modest 0-6 km shear values possibly as high as
30 to 35 kts may support isolated severe storms with primarily a
damaging wind threat along and ahead of the cold front in the late
afternoon and evening. The increased cloud cover and precipitation
will keep highs a few degrees cooler than Sunday.

Tuesday through Friday...will keep thunderstorm chances going
through the night into early Tuesday morning to cover the possible
slower frontal passage. After this...much of Tuesday through Wednesday should
be dry and cooler as high pressure passing to the north sets up
another period of easterly winds. This will limit highs to the 70s
while drier air leads to mins from the middle 50s to lower 60s. The
late Wednesday through Friday period remains low confidence as the European model (ecmwf) and
GFS differ in the handling and timing of subsequent middle level
shortwaves and placement of the returning warm front that will
influence rain chances. For now...our consensus blend approach will
keep chance to slight chance probability of precipitation for showers and thunderstorms over
especially the south through this period. Confidence is higher that
temperatures will be below normal with highs from the middle 70s to
lower 80s with overnight lows in the 60s.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1129 PM CDT Friday Jul 3 2015

Generally VFR conditions next 24 hours with fair skies of a milky
complexion from Canadian wild fires smoke and light winds the next
24 hours as high pressure overhead dominates. Some light aviation
fog possible late overnight until early Saturday due to calm winds.


Dvn watches/warnings/advisories...


short term...12
long term...sheets

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