Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
644 PM EST Tuesday Nov 24 2015
issued at 640 PM EST Tuesday Nov 24 2015
High pressure centered over the southeastern United States will
be sliding up to the northeastern part of the country tonight.
This will provide dry weather locally into Wednesday evening.
Skies will be partly cloudy with patchy fog possible overnight.
Lows tonight will range from the upper 20s in the north to the
middle 30s in the south. Highs on Wednesday will be in the 50s.
Short term...(this evening through wednesday)
issued at 312 PM EST Tuesday Nov 24 2015
Main concern in the short term period is fog potential again this
evening/overnight...however confidence is on the lower side with a
more widespread dense fog event like this morning. Southeasterly surface
winds will be fairly light through the evening...with a saturated
lowest 0.5k feet of the boundary layer. Visbys this afternoon still
hovering in a 4 sm range from br/haze across portions of the area.
However...surface gradient expected to tighten with slowly increasing
southerly winds through the overnight hours. My feeling is enough of
a surface gradient will keep lowest bl mixed enough to preclude
widespread dense fog. As a result...added patchy fog to the grids
overnight. Expect the best potential for fog to be in the 03-09z
timeframe across the areas that had dense fog into the late morning
Otherwise...bumped temperatures up a degree or two overnight from previous
forecast...more of a compromise between mav/lav/met/ece MOS. With rather
robust 975-925 mb warm air advection overnight...feeling is a decoupled bl will be
short lived with a rather quick drop in temperatures early in the
overnight...then perhaps a more steady temperature curve in through the
Skies expected to be mostly sunny. Bumped maximum temperatures on Wednesday up
a few degrees versus previous forecast...closer to MOS guidance...with
full sun and low level warm air advection ahead of approaching trough. Temperatures
outperformed forecast highs this afternoon...especially over the snow
pack...despite lingering fog/middle cloud deck...so confidence is on
the higher side to bump up highs for Wednesday.
Long term...(wednesday night through tuesday)
issued at 312 PM EST Tuesday Nov 24 2015
Only minor tweaks needed to previous forecast as models generally in
agreement on above normal temperatures through Thursday and increasing rain
chances into Friday.
Strong southerly flow will persist Wednesday night into Thursday...ushering in
increasing higher dewpoints and cloud cover. Have continued with chance
showers northwest Wednesday night but may need to add mention of fog and drizzle
as low level lift does begin to increase in west/northwest areas as the front
draws closer. Stronger argument for drizzle/fog on Thanksgiving day
but have kept with shower mention for the time being. Best rain
chances arrive Thursday night into Friday with much of the area
seeing quarter to half inch of rainfall. Only change Friday was to
keep categorical probability of precipitation 12-18z Friday vs trend to push precipitation out a touch
faster. Past couple of systems have had lingering showers/light rain
so feel best Route is to hold onto a bit longer with downward trend
Friday afternoon into evening.
Colder air will move in behind the system sending temperatures back into
the 30s for highs on Saturday. Gulf will remain open with southern
stream system set to surge north towards the region with large area
of warm air advection precipitation. Could be some mixed precipitation Sunday into
Sunday night as cold wedge remains...but guidance seems to suggest
all rain. Will keep all rain in grids for now and monitor
profiles in coming forecasts.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 636 PM EST Tuesday Nov 24 2015
Latest hires guidance have all trended toward VFR conditions
overnight with last few runs. Still a bit concerned that lingering
boundary layer moisture and retreating high will lend to some
patchy fog development this evening before gradient tightens and
winds begin to increase. This will be the difference compared to
last night when winds decoupled and temperatures dropped late. Have
included a tempo MVFR visible at both terminals with optimistic
conditions after 06z. Southwest gradient winds on Wednesday will
be in the 10 to 20 knot range.
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