324 
fxus63 koax 051931 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
231 PM CDT Sat Jul 5 2008 


Discussion... 
active period is again upon the region as upper-level ridging 
breaks down to the west. Subjective 12z upper air analysis 
indicates upper ridge centered across rockies...as well as upper 
trough moving across the Montana/Canada border...and another upper trough 
just offshore of British Columbia. 500mb heat falls up to 80m in northern Montana indicate 
flattening of ridge in the west. Middle-level temperatures were notably warm 
from ND/South Dakota southwestward through western Nebraska/western Kansas and westward through The 
Rockies...with 19c noted at 700mb in northestern Colorado. 850mb low was 
centered in northern Saskatchewan...with moist axis /12c+ dewpoints/ extending 
well northward from Texas through the ctrl plains into southern sask/mb. 850mb 
cold front was still well west across The Rockies...with weak 850mb 
warm front/wind shift evident from southwestern ND through South Dakota toward the 
Nebraska/Iowa border. West-southwesterly winds at 850mb were up to 45 knots in northestern 
Nebraska...and 30 knots across the Texas Panhandle to southwestern Kansas. Surface low at 19z 
was centered in ctrl ND...with secondary low developing in southeastern Colorado. 
Remnants of morning convection had moved southward into Kansas by 19z...though 
clouds were still holding back temperatures in southeastern Nebraska. 


Main forecast concerns are with potential for convection late 
tonight...sun/sun nt...and Monday/Monday nt...as series of upper troughs drag 
a front across the region. Initial round of thunderstorms is 
expected to fire this evening in ND and develop southwestward as far S as ctrl 
Nebraska. Storms dropping out of South Dakota and/or moving out of north ctrl Nebraska may 
work into northern County Warning Area tonight. Uncapped elevated instability is rather 
marginal but would support thunderstorms and rain tonight if something can work southward. 
Higher potential begins tmrw evening as initial front begins to move 
into eastern Nebraska/northwestern Iowa. NAM pushes front through a little further S 
than GFS...and have leaned toward a compromise solution for now as 
boundary placement will inevitably depend on influence from overnight 
convection to the north. In either case...slow-moving front will be 
draped across the area tmrw afternoon/evening as a weak wave ripples across 
the flattening upper flow. NAM/GFS indicate rather strong cap S of 
the front...with 700mb temperatures around 12-14c...despite strong 
low-level warming on the nose of strong srly flow /with surface temperatures 
forecast to jump above 90f and dewpoints climbing into the 70s/. Bulk 
shear is forecast to remain rather marginal /around 25-35 knots/ but would 
be supportive of multicell and possibly marginal supercell 
development. Corfidi vectors/bunkers rt-moving supercell motion not 
forecast to be terribly strong given weak middle-level flow along/S of the 
boundary...thus slower-moving storms could produce heavy rainfall. 
Otherwise...damaging wind/large hail would be the main threats tmrw. 


Frontal position is forecast to stall or make slow southward progress sun 
nt/Mon. Again...boundary placement is likely dependent on influence 
from convective outflow and is subject to vary from current model 
solutions. Deeper upper trough will move across ctrl plains on Monday 
aftn/evng...with convection again firing near the boundary but likely 
capped S. Dynamics become a little stronger with approach of upper 
trough...with both middle-level and upper-level flow strengthening 
somewhat. In addition...surface low begins to ripple up the boundary as a 
surface reflection of the trough. Bulk shear is still relatively weak 
/around 30-40 knots/ but is more supportive of supercells on Monday. 
Cooling middle-level temperatures should help increase middle-level lapse rates 
as well. Appears that severe potential is higher on Monday with attendant 
wind/hail threats...but location of highest potential is contingent 
on surface boundary location within the County Warning Area. Heavy rain is still a 
possibility on Monday...and between the two rounds of convection...will 
need to monitor Hydro conditions should boundary indeed remain in nearly 
the same location on both days. Upper trough should push front 
through County Warning Area on Monday nt/Tuesday morning...taking convective potential southward 
with it. Held onto schc probability of precipitation through midday Tuesday for any lingering 
activity. 


Confidence decreases quickly after frontal passage on Tuesday. Models 
mainly agree in passing an upper ridge across the central US while 
digging a trough into the western states...but differ in amount of 
amplification of the pattern. Latest runs do agree in building 
enough middle-level heat by the end of the week/next weekend to cap the 
MO River Valley and allow temperatures to reach back into the 90s. For 
midweek...European model (ecmwf) keeps storm track closer to County Warning Area...with County Warning Area on fringe 
of rain showers/thunderstorms and rain chances through Friday. GFS builds a stronger 850mb ridge 
and keeps the region drier through the week...with a few pockets of 
rain showers/thunderstorms and rain popping up associated with weak waves. With lack of 
confidence in timing any of those potential rain showers/thunderstorms and rain episodes...as 
well as disagreement among medium range models...will keep probability of precipitation dry 
for now...though do not expect as prolonged a dry period as grids 
might indicate. Kept temperatures near or just above climatology midweek before 
the climb into the 90s Fri/Sat. 


&& 


Aviation... 
for taf sites koma/klnk/kofk. 


Expect mainly VFR conditions outside of thunderstorm activity into Sunday 
morning. Thunderstorms are possible in the kofk area by around 05z...but 
not until closer to 12z for koma and klnk. MVFR ceilings and IFR 
visibilities will be possible with thunderstorms...but did not go that low 
just yet. Will amend as needed. South/southeast winds should 
continue through tonight ahead of the cold front. 


&& 


Oax watches/warnings/advisories... 
NE...none. 
Iowa...none. 
&& 


$$ 


Mayes/Miller