Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Des Moines Iowa
617 PM CDT sun Mar 9 2014
Short term /tonight/...
issued at 342 PM CDT sun Mar 9 2014
Warmup has been robust from relatively cold start across central
Iowa as southwest winds increased quickly. Strong mixing has
allowed readings to climb into the 50s to lower 60s in locations
without snowpack. Farther north...the snowpack is limiting
readings to the low to middle 40s with some help from high clouds
passing overhead. Pressure gradient will weaken overnight as trough
axis approaches the northwest toward morning. This will allow
winds to weaken some during the overnight although the relatively
warmer airmass will remain in place. Lows will be much warmer than
has been seen in some time with readings likely remaining at or
above freezing across the forecast area. Some middle and high
cloudiness will continue to stream overhead as well with strong
jet axis just north of the state.
Long term /Monday through Sunday/...
issued at 342 PM CDT sun Mar 9 2014
Forecast concern remained focused on temperatures for Monday and
precipitation chances on Tuesday. Models are in good agreement
through Tuesday and leaned toward a blend for timing on precipitation
Monday...warmest day of the extended looks to be tomorrow as the
850mb warm nose nudges into southern Iowa Monday morning. 850mb
temperatures ranged from +10c to +14c throughout the day...and even with
surface high moving into the state and causing weak cold air advection by the
late afternoon...temperatures should have no trouble rising well
above normal temperatures for central to southern Iowa. The
snowpack areas will still be cooler...but tweaked maximum temperatures up
slightly where much of the snow pack was lost today. Generally
went 5 to 6 degrees above the warmest guidance for maximum temperatures
Monday over the central to south.
Tuesday through Wednesday...surface low pressure prognosticated to
develop over Colorado and transitions east across Kansas and into
Missouri through the day Tuesday. A decent deformation zone
develops over northern Iowa Tuesday as there is moderately strong
frontogenetical forcing between 600-650mb over northern Iowa per
GFS and NAM is stronger in the 750-700mb layer. The cold air advection looks to
develop sooner and will transition the rain to snow quicker by
early Tuesday afternoon resulting in slightly higher snow amounts
in the north. Have roughly 2 to 3 inches forecast across the far
north. Soundings look to be either snow or rain...and left out any
mention of sleet at this time as there is no indication of a significant
warm layer aloft to cause any melting. The cold air advection looks strong
enough to quickly cool the column through the late morning into
the afternoon hours. Plus the web bulb temperatures remains near freezing
much of the day. Kept mention of non-diurnal temperature
trend and cooled temperatures across the north sooner to handle
the cold air advection developing Tuesday morning.
Cold air advection continues on Wednesday and increased winds a few knots and
cloud cover to handle the low level moisture advecting into the
state. Also cooled temperatures slightly for maximum temperatures.
Thursday through Saturday...benign weather pattern through the end
of the work week as surface high builds into the region and
500mb zonal flow to slight northwest flow persists through
Saturday. Trended slightly warmer for maximum temperatures on Thursday...but
overall no major changes.
issued at 617 PM CDT sun Mar 9 2014
Winds will diminish some through 02z and lose their gustiness. An
upper level disturbance will sweep across the north and east late
this evening through 14z Monday. VFR ceilings are expected with this
feature then as it passes the surface wind will switch around to the
west to northwest.