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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
958 am CDT Friday Jul 11 2014

issued at 958 am CDT Friday Jul 11 2014

Cluster of thunderstorms in western Iowa on the nose of a 40 knot
low level jet early this morning has shifted into central Iowa but
has the low level jet weakens. Expect a continued
weakening of these storms this morning but there will be plenty of
debris clouds. Will maintain small probability of precipitation today as forcing looks
weak and will monitor temperatures and cloud trends.

Update issued at 641 am CDT Friday Jul 11 2014

Sprinkles with perhaps some isolated light showers continue across
the area falling from a 12 kft cloud deck. As the overall forcing
weakens this morning...the sprinkles/showers will end leaving just
clouds across the area. The potential for diurnal convection this
afternoon is dependent upon how much daytime heating occurs.

Update issued at 400 am CDT Friday Jul 11 2014

The forecast has been updated to reflect isolated to scattered
showers for the pre-dawn and morning hours.

Sprinkles/very light showers are occurring out of 12 kft bases.
Thus the dry air is not as extensive as suggested by the models.


issued at 234 am CDT Friday Jul 11 2014

06z surface analysis has weak lows in the Dakotas with a slightly
stronger low in southeast Colorado. A stationary front ran from the
Oklahoma Panhandle into the deep south. Dew points were in the 50s
across the Great Lakes with 60s in the plains. Dew points in the 70s
were across the deep south and lower Mississippi Valley.


Short term...(today and tonight)
issued at 234 am CDT Friday Jul 11 2014

Dry conditions will be seen through sunrise as a thunderstorm
complex moves into northwest Iowa. A Wing of elevated showers from
southern Minnesota into northeast Iowa should slowly decay as it
encounters drier air over eastern Iowa.

A majority of the area will see dry conditions during the morning
hours as the overall forcing weakens considerably and any convection
encounters dry air. The exception looks to be the far northwest and
Highway 20 corridor west of Dubuque where some isolate showers may
be possible. However...given the amount of dry air across the area
the possibility does exist that this area may remain dry as well.

Overall forcing is extremely weak during the afternoon hours and
there should be a respectable shield of high clouds to help suppress
temperatures somewhat. The question becomes will it get warm enough
to allow diurnal convection to develop with what little forcing is
present. Based on projected soundings...the chances for diurnal
convection is not good but have opted to go with low end slight
chance probability of precipitation for some isolated convection.

Tonight...a boundary develops across the area and the overall
forcing increases during the evening along with available moisture.
Thus isolated convection will slowly become more numerous during the
evening with storms growing upscale into one or more organized
thunderstorm complexes after midnight. The more favored area for
rain would be the northern half of the area and rainfall could
become locally heavy in spots.

Long term...(saturday through thursday)
issued at 234 am CDT Friday Jul 11 2014

Good chances of showers and thunderstorms this weekend...then near
record cool temperatures early to middle of next week.

Overview...initialization and verification good on upper air energy
with American solutions especially too moist in bl as is often the
case. Mostly minor differences all solutions on large scale flow
and thermal to run variance suggests using a 60/40
mix of GFS with hi-res European model (ecmwf)/Gem-NH blend. This portends a decent
mesoscale convective system event late Saturday into Sunday and to a lesser extend Sunday
PM with mostly moderate to lower end heavy rain totals and
isolated severe in PM hours with enough heating this weekend.

Saturday and Saturday night...favorable jet structure and moisture plume
and forcing for likely probability of precipitation over at least north and central sections.
Precipitable water values of 1.75+" suggested with progressive shear and jet supports
limited training though. This should result in .5 to 1.5 inches of
rain with locally 2 inches. This with our past dry weather for over
a week support limited or no water issues unless we get heavy rain
totals Friday...which appears very unlikely. Later shifts will need
to reassess severe risk as heating with the key as thermal fields
suggest need highs well into the upper 80s for isolated severe for
mainly winds which with cloud cover may not occur. Any severe should
be at the low end unless phasing of upper trough digs more for strong
low level convergence along frontal boundary. Highs Saturday with
convection should be 2-3 degrees above convective temperature or
middle to upper 80s. Saturday night lows will be impacted on evaporative
cooling with mesoscale convective system event with mins possible needing trimming by a
few degrees with any cool pools or middle to upper 60s are possible.

Sunday...frontal passage during the day with question how much convection
to fire middle/late day and confidence poor as prior convection will impact
on how widespread and strong the precipitation could be but risk are
low at this time due to "anafront" nature of shear...or northwest flow. Highs
mostly in the middle 80s with falling PM dewpoints on northwest winds of 10 to
20+ miles per hour. Sunday night...clearing and turning cooler late with lows with
cool front per local thermal fields likely needing lowering by 3 plus
degrees...or middle to upper 50s.

Monday through Wednesday...near record cool Canadian high pressure to
impact area with breezy northwest winds Monday and probably Tuesday in the
afternoon with gust to 30 miles per hour possible with strong bl mixing. Highs
based on thermal fields may need trimming by up to 3 degrees...especially
Monday with lows 2 to possibly over 5 degrees too mild...with decoupling.
This could approach record mins Tuesday/Wednesday am. Generally highs of 66 to
77 degrees are suggested and lows 45 to 55 degrees Tuesday/Wednesday am.

Thursday...return flow starts with temperatures upper 70s to around
80 degrees suggested...still several degrees below normal with lows
Thursday am still in the middle/upper 50s.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 641 am CDT Friday Jul 11 2014

VFR weather is expected through 03z/12. Vcsh are possible at kcid/kdbq
through 18z/11 followed by thunderstorms in the vicinity at all taf sites after 20z/11. After
03z/12 VFR conditions are expected to continue but thunderstorms and rain will
become more widespread with time. The potential does exist for
MVFR conditions to develop after 03z/12 as thunderstorms and rain become more numerous.


Dvn watches/warnings/advisories...


short term...08
long term...Nichols

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