Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
707 am CDT Sat may 23 2015

Update...
issued at 658 am CDT Sat may 23 2015

Updated to include 12z aviation discussion below.

&&

Short term...(today and tonight)
issued at 258 am CDT Sat may 23 2015

The upper level trough centered over The Four Corners region this
morning is the feature of concern for the period. It is still on
track to lift northeast today and tonight...but its speed in doing
so looks a tad slower at this time. So...the primary changes to
the short term forecast was to just delay the probability of precipitation a few hours
across the area.

The latest hi-res guidance indicates a narrow band of rainfall
pushing north into southwestern Minnesota this morning...thanks to low
level warm air advection ahead of the approaching trough. Forcing
though will not be impressive and very dry air under the local today
will hamper the ability of this band to produce measurable
precipitation. This band may be primarily virga...so did reduce
probability of precipitation into the slight chance category. Most of the forecast area will remain
dry today...but mostly cloudy under the middle and upper level moisture
feed from the southwest...so temperatures will be slightly cooler
than yesterday...but still expect highs around 70 for most of the
area.

For tonight...slowed down the onset of the precipitation as general
consensus of the models agree on a slower progression into our
area. In fact...the 00z run of the European model (ecmwf) now keeps eastern Minnesota and
western WI completely dry through 12z Sunday...and the arw-east
matched up well with the European model (ecmwf). Current forecast has trended that
direction as the main precipitation shield is not expected to impact most
of the area until during the day on Sunday.

Long term...(sunday through friday)
issued at 258 am CDT Sat may 23 2015

More widespread precipitation comes Sunday as a deep 500 mb low pressure
center over the central rockies contributes to a developing surface
low pressure center over the west-Central Plains. A large plume of western
Gomex moisture will continue to surge into the region on the western
side of a large southeastern Continental U.S. 500 mb high pressure dome...so the surface and
aloft low pressure combination drifting northeastward will have plenty of
moisture with which to produce periods of showers/T-storms over the
region from middle-to-late day Sunday through Monday night. The surface low
looks to take a track that will bring it from eastern Colorado/western Kansas Sun
afternoon into central Minnesota by daybreak Monday morning while the kicker upper level
low will coincidentally shift northeastward into the eastern Dakotas. The
tilted aspect of the low within a deeply moist environment will
provide plenty of isentropic lift on its leading edge to produce
fairly widespread rain Sun night into Monday. This additional
moisture into the atmos...even near the surface as evidenced by
forecast dewpoints into the lower 60s...may add some fuel to the
potential of strong/severe storms on Monday. Expansive cloud cover
and meager lapse rates may well put a damper on such potential but
between Sunday and Monday...Monday looks to be the better day for
any strong/severe storms. However...with precipitable waters around 1.50 inches
and a prolonged nature of this system...isolated pockets/periods of
heavy rain cannot be ruled out for Sun night into Monday.

The surface low and upper level low pressure features will pull away to NE on
Tuesday...allowing for a diminishing of precipitation coverage and intensity
Tuesday through Wednesday...with some Bona fide dry time likely for much of the
area during this time. The Wednesday-Friday timeframe has a much
higher degree of uncertainty due to the upper level flow becoming
more zonal and a surface pattern that has less definition. Several
upper level shortwaves passing through the region from time to time will
be most responsible for shower/thunderstorm development during the latter
half of the week...so have capped probability of precipitation in the chance category to
allow for better model agreement before locking on a period worthy
of a likely pop.

As for temperatures...the theme of little day-to-day variation
still holds true. It does look that Wednesday will have the
highest temperatures throughout the upcoming week...with highs
hitting the upper 70s. This does make sense with a southerly surface flow
resuming after the departure of the early week storm system and a
mix of sun and clouds expected for Wednesday. Otherwise...temperatures will
generally range from the middle 60s to the middle 70s...still rather
comfortable for late may. Lows will mainly remain in the 50s.

&&

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 658 am CDT Sat may 23 2015

High clouds blanket all taf sites this morning in advance of an area
of low pressure developing over the plains which will have more
significant impacts Sunday and Monday. For today...clouds will
steadily lower throughout the day and tonight but remain at VFR
levels. Kmpx radar currently shows a swath of -shra moving into
southwestern Minnesota...with a scattering of ob sites reporting -dz/-ra. Given
its northeastward trajectory...have included a short duration of VFR -shra
at the 4 Minnesota taf sites while keeping the 2 WI taf sites dry.
Broken/overcast decks will prevail tonight into tmrw morning...with krwf-kmsp
having the best chances of seeing precipitation prior to 12z tmrw morning.
Light/variable winds this morning will become generally southerly by midday
before gradually backing to east-southeast tonight with speeds at or below 10 kts.

Kmsp...few -shra possible between 16z-20z today...but could be
slightly earlier if anything. Regardless...the precipitation today would be
insignificant. More widespread and heavier precipitation is expected late
tonight through midday tomorrow and Onward.

/Outlook for kmsp/

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

Update...jpc
short term...speed
long term...jpc
aviation...jpc

National Weather Service Glossary of Abbreviations