Area forecast discussion
National Weather Service Des Moines Iowa
639 am CDT Thursday may 23 2013
Short term.../today /...
issued at 313 am CDT Thursday may 23 2013
Upper low will move out of the area today as surface trough
extending from northern Illinois into northwestern Iowa rotates south across the state
this morning. Isolated to scattered showers over the east half of
the County Warning Area should come to an end early this morning as drier air
begins to push south behind the trough. High pressure centered
over northern Manitoba will push south today. This will bring gradual
clearing from the north today. Cool 800 mb air for this time of the
year will put a limit on the high temperatures today with forecasts of +3 to
+7 across the state this afternoon. Sunshine should overcome the
cold air advection and give highs in the 60s across the County Warning Area this
afternoon.
Long term.../tonight through Tuesday/...
issued at 313 am CDT Thursday may 23 2013
Little has changed in overall forecast thinking this shift.
Tonight and Friday will remain dry and uneventful with a large
surface high pressure center sliding from The Arrowhead of
Minnesota across Wisconsin and into the Great Lakes region. This
will result in northeast winds this evening becoming calm or light
and variable...then turning around to south southeast on Friday.
With calm/light winds and dry air filtering out of the high
pressure area temperatures will drop to well below seasonal levels
tonight especially across our northeastern counties where Friday
morning lows in the upper 30s are forecast in some areas.
However...temperatures are not expected to reach levels sufficient
for frost formation.
By Friday night the axis of the central U.S. 500 mb ridge will be
located over Iowa...while a large 500 mb low centered over the
Pacific northwest will have carved out a deep but broad trough
down the West Coast. This general pattern will then remain in
place through the entire remainder of the seven day forecast. This
will lead to an overall wet and active forecast for the area this
weekend and the first half of next week as a train of middle-level
impulses move up the southwesterly flow on the western flank of
the ridge and over the midwestern states. Unfortunately any
attempt to pin down the precise timing and location of these
impulses...much less the precipitation they produce which will
also be dependent on the location of subtle surface boundaries and
other difficult to predict features...is futile at this point.
Therefore the forecast remains peppered with probability of precipitation for the
foreseeable future. From Friday night through Sunday have
maintained probability of precipitation generally in the 40 to 60 range...which then
decrease steadily into next week as confidence decreases further.
The good news is that the overall synoptic set up does not lend
itself well to large severe weather events...however at this time
of year such a prolonged period of thunderstorm chances implies
that some degree of severe weather will probably be achieved at
some point. In addition...heavy rain could result in localized
flash flooding and possibly larger scale areal flooding depending
on whether thunderstorms form over the same areas day after day or
shift around the region a bit.
&&
Aviation...23/12z
issued at 636 am CDT Thursday may 23 2013
Low pressure trough kmli-kdsm-kykn line will move south of the taf
sites this morning. IFR and MVFR ceilings will push south with the
trough with clearing reaching the southern sites by early afternoon.
High pressure over northern Manitoba will build south with clear
skies and diminishing winds for tonight.
&&
Dmx watches/warnings/advisories...
none.
&&
$$
Short term...MS may 13
long term...Lee
aviation...MS may 13
