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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
649 am CDT Tuesday may 26 2015

issued at 332 am CDT Tuesday may 26 2015

Showers are perculating over northeast Iowa early this am in wake
of passing outflow boundary. Overall... rain chances will be
increasing today as a shortwave trough over Kansas/OK lifts northeast
into the upper Midwest while merging with remnant upper level low
shifting east from NE. Isentropic ascent...vorticity advection...
increasing low level convergence with passing mesoscale-low along with
surge of moisture/Theta-E ridge with precipitable water values climbing to near
1.5 inches will all result in fairly good coverage of showers as
day progresses with a few storms as well. Weak cool front/surface
trough to move into the area tonight and should result in tapering
rain chances.


Short term...(today and tonight)
issued at 332 am CDT Tuesday may 26 2015

Increasing coverage of showers and a few storms expected this am
with forcing and moisture advection ahead of approaching shortwave
and surface meso-low. Locally heavy rain will be the main
concern... with the focus for higher rain amounts (potentially
pockets of rainfall of 1-2 inches) being over the western County Warning Area...
especially northwest of remnant outflow boundary from near iow-
dbq where lift is maximized with increasing convergence from
approaching mes0-low and upper level diffluence ahead of
shortwave. Cant rule out some flooding issues being possible
especially with any training and prolonged bouts of higher rainfall
rates. This afternoon it would appear as though greater coverage
of precipitation will migrate north of I-80 as system lifts through the
region and middle level dry intrusion envelops much of the area.
This may allow for some partial sunshine which could allow for some
destabilization and development of scattered showers and storms.
Sufficient shear with 0-6km bulk shear 30-35 kts for potential of
a stronger storm or two should sufficient destabilization occur. As
for highs today... as the clouds/precipitation go... so go the temperatures and
therefore a tricky temperature forecast with bust potential. Have nudged
down highs 1-2 degrees northwest County Warning Area where likelihood of more rain
and lingering clouds and have around 70 or lower 70s there with
middle/upper 70s elsewhere.

Tonight... anticipate gradual tapering of rain chances with focus
shifting more to the south in time as weak cool front/trough
moves into the region. Lows coolest northwest (mid/upper 50s) to
warmest southeast (lower 60s) under partly to mostly cloudy skies
and light southwesterly winds.

Long term...(wednesday through monday)
issued at 332 am CDT Tuesday may 26 2015

Main forecast concern for the long term forecast are
the chances for probability of precipitation at the beginning of the period and then the
chance for probability of precipitation this weekend. Active weather pattern remains in
place across the area through the long term with chances of probability of precipitation
virtually every day with the exception of a short period Wednesday
into Thursday.

Wednesday...the current trough that has plagued the central United
States for the past week or so finally ejects out of the plains.
This occurs because another trough is building in from the northwest. This
gives US only about 24 hours of 500 mb ridging until the next trough turns
the flow to the SW on Thursday. Wednesday afternoon into Thursday
late afternoon should be quiet and pleasant.

Thursday the flow turns south-southwest across the area. This should usher
moisture and shortwaves into the area again for Thursday night into the
weekend. The models...especially the spectral models with larger
grid spacing seem to be overdoing it with coverage of the probability of precipitation.
They have done it with the current system. This could be due to the
convection downstream south of here or issues with parametrization
schemes. Regardless...they depict diurnal convection. The NAM
seems to be the best as far as coverage of probability of precipitation. This suggests that
Thursday most of the showers and storms will be west of the area
until near 00z. After 00z Friday showers and storms will advect
into the area and likely affect northwest zones the most Friday night.

Overall timing and structure of the forcing appears to be consistent
through 12z Saturday. There are small differences but nothing that
would affect a forecast this far out. Those differences would
likely affect mesoscale features that are inherently difficult to
forecast this far out. The overall trough is slow to leave the area.
Cooler air will be pulled into the area Sunday...leading Sunday and
Sunday night being chilly.


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 638 am CDT Tuesday may 26 2015

Showers and a few storms will be found this am with MVFR to local
IFR conditions. The rain will taper off from south to north middle
morning through early afternoon. Will have a chance at scattered
showers and a few storms this afternoon and evening ahead of a
weak surface trough... but low confidence on occurrence at
terminals thus have left out any mention of this chance for now.
Conditions expected to improve to VFR this afternoon and remain
generally VFR through tonight...with MVFR conditions in any
scattered shower or storm activity. South to southeast winds
around 10 kts and gusty at times will veer to southwest 10-20 kts
this afternoon then diminish below 10 kts tonight.


Dvn watches/warnings/advisories...


short term...05
long term...Gibbs

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