Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 181855

Area Forecast Discussion
National Weather Service Northern Indiana
155 PM EST Sun Feb 18 2018

Issued at 320 AM EST Sun Feb 18 2018

A very wet week is ahead with warm temperatures just down the
road. Highs will climb to near 60 Monday, and then even warmer
Tuesday with highs near 70. A rainy period from Monday into
Wednesday will cause rises on rivers with flooding on many. In
addition to river flooding, areal flooding is also likely
particularly over low lying and other flood prone areas.


.SHORT TERM...(This Evening through Monday)
Issued at 153 PM EST Sun Feb 18 2018

Brief period of quiet weather this evening to begin the short
term period. Surface high pressure sliding quickly eastward in
fast moving zonal flow aloft over the northern US...this will set
the stage for increasing southerly return flow moving up into the
region. Very dry low levels on 12Z soundings this morning
indicative of large scale subsidence beneath surface high and will
delay onset of precip tonight as initial moisture surge will be
to our west up along MS river valley. Theta-E ridge axis will
extend up into the mid MS valley this evening before shifting
eastward over our area by 12Z Monday. Strengthening S/SW flow with
nose of 50kt LLJ impinging on the area by early morning Monday
and accompanied by 75kt mid level speed max will coincide with
saturated column in the low levels to bring precip chances to the
area from west to east after 06Z Monday and continue over the
entire CWA through remainder of short term period. Quasi-
stationary frontal boundary to the NW of our area will allow
continued surge of warm moist air into the region with 850mb temps
and dewpoints reaching 10C by Monday afternoon. Could definitely
see some convective elements embedded within widespread light to
moderate rain but deep SW surge of warm air thru the mid levels
will limit mid level lapse rates and potential for thunderstorm
development. WAA associated with increasing southerly flow will
have temps steady/slowly rising after midnight and highs Monday
will reach 55-60F.


.LONG TERM...(Monday Night through Sunday)
Issued at 153 PM EST Sun Feb 18 2018

Multiple rain chances continue into the long term period.
Anomalous upper level ridge just off the SE coast continues to
strengthen up to 3 standard deviations above normal Tuesday/Tue
nite keeping trough over the SW US and resulting in a SW mean flow
nearly parallel to slow moving frontal boundary. Continued surge
of moisture ahead of this front will have PW values approaching
1.5 inches...these value will reach in excess of 300 percent of
normal for this time of year and sounding climatology suggests
near record values. SW low level flow continues and even increases
as 60kt+ LLJ will be paralleling approaching frontal boundary
Tuesday afternoon and evening. While instability remains
marginal...still expecting embedded convective elements and near-
parallel flow will have slow moving meso-beta elements which will
bring potential for localized heavy rain and flooding. Latest
model trends with placement and timing favoring our NW CWA for
this setup...with timing favored toward approach of frontal
boundary Tuesday afternoon/night. With that in mind...and with
only a couple forecast points expected above minor flooding...plan
to hold off on any headlines attm. Unseasonably warm temps
continue Tuesday with 30F above normal highs and near record
values possible. Mid-level short wave ejecting out of SW US trough
is expected to be sufficient to push frontal boundary through the
area on Wednesday. While large scale pattern still maintains
upper ridge to our SE and troughing over the western US...surface
ridging building into the great lakes region may keep quasi-
stationary boundary suppressed far enough south along the OH/TN
valley to allow for period of dry weather at least Thursday and
possibly longer. Additional energy ejecting out of western trough
will act on frontal boundary and bring additional precip chances
toward the end of the period with uncertainty lying with ultimate
placement of the will limit POPs to chance range for


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 1217 PM EST Sun Feb 18 2018

MVFR conditions under stratus deck at the onset of the forecast
period. Low clouds will scatter out and bring conditions back up
to VFR. Low level wind shear increases this evening as southerly
winds at surface veer and increase with height to out of the west.
Rain enters the area after 08z lowering cigs down to MVFR. Some
guidance indicating heavier rain by morning further lowering cigs
and vsby to IFR. Left out of forecast due to lower confidence.





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