Area Forecast Discussion
Issued by NWS Des Moines, IA
FXUS63 KDMX 291741
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1241 PM CDT Thu Sep 29 2016
Issued at 333 AM CDT Thu Sep 29 2016
No major concerns through the morning and daytime hours today
with mostly clear skies, lighter northerly winds and gusts around
7-10kts and 15kts respectively, and warmer temperatures in the
upper 60s to around 70 prevailing. Only concern exists in the near
term regarding fog/low stratus development. With the clearing out
of the daytime/evening stratus deck yesterday, it has paved the
way for inversion development and moisture trapping near the
surface. Currently, all hi-res guidance keying on the development
of fog/stratus across the northern third to half of the state and
scattered elsewhere around 9z, before dissipating shortly after
sunrise. Given still saturated grounds across that region, cannot
wholly disagree. One potential factor against widespread fog
development will be winds, as many locations remain at or just
above 5kts and may remain so through morning. Small patch of
stratus in SE MN has show slow growth S/SW and will likely
continue through just after sunrise. Have peppered the grids with
patchy fog and increased cloud cover, but not overly confident it
will have the areal coverage depicted.
.LONG TERM.../Tonight through Wednesday/
Issued at 333 AM CDT Thu Sep 29 2016
Main concerns during the long term period include precip chances
Friday night into Saturday as well as from Tuesday night into
Upper-level low will be drifting northward at the beginning of
the long term period. By 12Z Saturday the low will be centered in
the vicinity of central Indiana, and by 00Z Sunday it will be
centered in the vicinity of the Michigan/Indiana/Ohio common
border area. Thereafter it will lift northeast as the western U.S.
trof begins to move onshore along the Pacific Ocean.
For the eastern CWA, have slight chance POPs on Friday night, and
slight chance to low-end chance POPs on Saturday due to presence
of ample lift and moisture with the upper-level low being closer
to the CWA. Although the POPs will be confined to the eastern CWA,
the entire CWA will see significant cloud cover on Saturday. The
cloud cover will linger across much of the CWA into Sunday though
as the upper-level low lifts northeastward. An upper-level ridge
building into the CWA region from the west will help decrease the
cloud cover with drier air and downward vertical motion during the
day on Sunday.
Next chance of precip will come on Tuesday as the western U.S.
trof moves onshore and traverses the Rockies. Have backed off on
timing of the precip arrival due to slower model solutions. Best
precip chances will be Wednesday into Wednesday evening as the
trof axis swings through the CWA, pulling a cold front through
with it at the surface. Depending on timing of the surface
boundary, conditions may be favorable for a progressive severe
weather event such as a QLCS as mentioned in the earlier AFD.
Although instability will not be impressive, shear will be
sufficient for organized convection.
Temperatures during the long term period will average out to be
near to slightly above climatological values, with some deviations
both above (especially the Monday-Tuesday timeframe) and slightly
below (mainly the Friday-Saturday timeframe) normal.
.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1240 PM CDT Thu Sep 29 2016
Once KFOD stratus clears shortly, there will be a high confidence
in VFR conditions at all sites through the evening hours. However
confidence decreases somewhat into early Friday morning due to fog
and stratus re-development uncertainties. For now have included
MVFR fog at KFOD until confidence increases, but lower and more
widespread conditions are possible.