Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
523 PM CDT Thursday may 23 2013
Short term...through Monday
issued at 204 PM CDT Thursday may 23 2013
23.12z radiosonde observations show good 925-850mb cold advection across the western Great
Lakes this morning in moderate northeast flow. Frontal slope over
the state is something that will come into play for upcoming
forecast and how far it slides southwest. At 12z kinl-kabr had a 7c
temperature difference at 850mb /12c at 925mb/. A massive drying
across Minnesota occurred overnight with precipitately water values
plummeting from 0.90 to 0.32 inches...or 136 to 48 percent normal.
The surface ridge nosing in is quite dry with precipitable water
values in the 30 percent range across southern Canada. This gave way to a
sunny but cool day today. A higher amplitude ridge axis is
anchored in the Dakotas and south...while a deeper cyclone has now
shifted onshore into the northwestern U.S. Numerous spokes of energy are
circulating around that low...one of which is quite strong over
Nevada with rap analysis showing a tropopause fold to near
500mb...on the poleward side of a measured 100kt 250mb jet core
nose. This is driving height falls across Mt/ID/UT. Surface dew
points of meaning for convection are located in Oklahoma...soon to
return northward.
Forecast is on track for calming winds tonight and clear skies.
Widespread frost should occur with lower 30s forecast across northwestern
WI. With lower dew points over northwestern WI counties currently...have
decided to just add all of those counties into the frost advisory.
Big picture during this period is falling heights and pressure in
the Front Range with southerly flow increasing and a return of
moisture to Nebraska/South Dakota Friday night. This will place the low-level
thermal boundary across the forecast area from 850-925mb...slightly
displaced swwrd...from kabr-kmli. The consensus NCEP models at
23.12z remain consistent with their previous runs on the frontal
boundary becoming active in the Dakotas/Nebraska Friday evening and
shifting east into Minnesota/Iowa overnight. The 23.00z European model (ecmwf)/UKMET
solutions do as well...however they remain further west.
The 300/305k surface in the NCEP solutions remains consistent with
an 8g/kg moisture surge isentropically lifting and converging into
central and eastern Minnesota Friday overnight with a fetch of about 500 j/kg
of MUCAPE feeding it. The NAM seems to be the most agressive. Not
overly impressive for severe weather...but rather there is enough
forcing to generate rain/thunderstorms and rain swwrd of msp. The European model (ecmwf) solutions
suggest more of a focus in southern/southwestern Minnesota. The main question is how
far east does this convective complex track Friday night and how far
east does the frontal boundary lift. Have increased rain chances
further east for Friday night and Saturday...however with the
verification record of the European model (ecmwf)...there is still a chance the
eastern areas will be dry. Confidence is low on the exact
location of the weather...but higher that it will be an active
frontal zone with rain showers/isolated thunderstorms and rain.
This question remains through Monday...how far east will the
frontal band be located. The front will likely remain active with
showers/storms and clouds...and highs quite a bit cooler thanoutside
the band. Overall...have increased rain chances in the western/southern
forecast area and tried to remain nearly dry in the east. Seems
like it will be a cloudy weekend...and thus have lowered highs
Sunday and Monday as well. Severe weather threats are most
possible in southwestern Minnesota closer to the cape pool...and Monday looks
most favorable should the instability increase as the warm front
moves toward Minnesota. However...activity along that front this weekend
may have much to do with how the environment/front evolves Monday.
Long term...(friday night through thursday)
issued at 241 PM CDT Thursday may 23 2013
It continues to look like we/ll unfortunately need to keep a
prolonged period of chance probability of precipitation in the forecast through the week
as the baroclinic zone lingers in the area... with elevated
instability and persistent warm advection work to generate
scattered shra/tsra. There will undoubtedly be some dry periods...
with precipitation focused when individual shortwaves ripple southeast
through the upper flow... but at this point it is impossible to
try and Pin Point when such dry periods might occur. The 12z European model (ecmwf)
has come around more in line with the GFS in keeping things more
active in our area throughout the time period... although both
suggest we should finally bring the upper trough east toward the
region by the end of the week. Depending on how that unfolds... we
could have a possibility for focused convection and possible
severe weather during the Thursday-Friday time frame. But... until
that point the main issues would likely be locally heavy rain and
perhaps some hail. In general... temperatures will warm through
the week as the bonafide warm sector slowly lifts north into the
area.
&&
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 459 PM CDT Thursday may 23 2013
VFR during the period. Increasing high clouds from the west during
the day Friday. Chance of rain showers limited to far western sites.
Introduced vcsh for now. Light northeast to east winds becoming
southeast overnight and increasing on Friday. Gusty at Minnesota sites by
midday.
Kmsp...
VFR through period. Next chance of showers moves in later Friday
night. Light northeast to east wind becoming southeast Friday and
a bit gusty by midday.
/Outlook for kmsp/
Friday night...VFR. Chance of showers. Southeast wind 5 to 15 knots.
Saturday...brief MVFR ceilings possible with a chance of
shra/tsra. Southeast wind 10 to 20 knots.
Saturday night...MVFR ceilings and visibilities possible with a
chance of shra/tsra. Southeast wind 10 to 20 knots.
Sunday...MVFR ceilings and visibilities possible with a chance of
shra/tsra...brief IFR conditions possible. Southeast wind 10 to 20
knots.
&&
Mpx watches/warnings/advisories...
Minnesota...frost advisory from midnight tonight to 7 am CDT Friday for
mnz045-052-053-063.
WI...frost advisory from midnight tonight to 7 am CDT Friday for
wiz014>016-023>028.
&&
$$
Short term...baumgardt/arx
long term...
aviation...Delaware
