Archive for June, 2011

Arlene and the heat

June 30, 2011

1. tropical storm Arlene is heading into Mexico today and will have no impact on our weather to the broad observer. My thinking is looking at the strong ridge over the plains as a bubble it will bend it on it’s southern side. This could be a cause in a northeast surge of the ridge over the weekend.

2. A frontal boundary may attack this boundary for storm chances by Sunday. Otherwise expect highs near 90 and lows in the 60’s to low 70’s with hot and humid conditions. sinking air  along with lack of a boundary will prevent storms despite the hot and humid airmass till Sunday. Will update this weekend regarding the 4th and the next potential front.

added 2 pm Thursday
– I’m concerned temepratures Saturday may be a touch warmer say mid 90’s in spots this coupled with dewpoints from 70-80 may make for some heat index values

Bowling green modeled max heat index values for Saturday

ECMWF 00z- 112

NAM 12z- 105

GFS 12z- 104

another MCS on the way

June 27, 2011

A severe thunderstorm watch has been issued this afternoon for regions southeast of LEX. Another cluster of storms will take advantage of high shear and moderate convective available potential energy (CAPE) ahead of it as it moves across the southern half of the region. steep lapse rates temperature difference with height associated with this cluster suggest storms could produce hail and high winds in addition to the high amounts of shear suggesting an isolated tornado threat. Tuesday may feature more storms with clearing and hot conditions for the remainder of the workweek with highs near 90 and lows in the upper 60’s to low 70’s.

Central Great Lakes sector loop

 

MCS likely Sunday

June 24, 2011

Eventhough storms were only scattered Thursday enough shear and instability in what i characterize moderate values were present. This led to a few storms producing gusty winds and a rotating wall cloud in Morgan county. The storms in the Lexington region were not tornadic and I’m not sure what gave the indication these storms were tornadic.

read above for the general forecast. However heading into Sunday I’m seeing the likelihood of a MCS complex and based on modeling I suspect precip chances Sunday to be going up in most forecasts. I’m not certain of the timing but this the type of situation that can lead to wash outs of outdoor events in addition to severe weather and flooding.

So far this severe season we started early with events that has considerable shear and little instability. Once summer sets in we went to a lot of events with high instability and little shear. Both of these scenarios produced severe storms with numerous events. the deep south tornado outbreak was an example of extreme shear and instability thus the major outbreak. now in recent days we have had moderate shear and instability which promotes some severe weather and tornadoes but not a widespread outbreak.  Parameters were just in the range needed for rotating storms not too much or to little. Yes folks you can have too much shear.

My concern already extends into this likely MCS Sunday particularly in regions that see some sun to destabilize things early.  If the mcs comes through early then a heavy rain and isolated wind damage threat would occur if it’s later

– lapse rates should steepen throughout the day showing an unstable atmosphere by days end, CAPE values becoming rather high as well showing moderate to strong instability

– bulk shear values of around 40,  and helicity values of 100-200 could lead to strong updrafts with storms and shear needed for rotation

– the MCS will be the boundary and lift for storms in a warm and humid airmass

again all of this is timing I fully expect the SPC to place the region in a day 3 risk for severe.

 

same stormy pattern

June 22, 2011

1. first let’s recap Tuesday’s forecast yes my critics will quickly point to this awful forecast Tuesday. Put it simple a shortwave provided lift well in advance of the front needed for storm development. other parameters favored storm formation but without lift nothing happens. This shortwave led to the big bust with regards to the forecast for most of the region. Also this forced what i was thought was a unwarranted  postponement of the reds-yanks game Tuesday night as leaving the stadium at 7 seeing postponed and the sun coming out doesn’t make much sense. Over the last few days of more concern is the tendency for storms to produce flooding rains and even some severe storms thanks to the instability and marginal shear in place. Louisville metro was hit hard with these storms Wednesday night. Also localized flooding in eastern Kentucky as hit some communities hard as well. Always look in the comments for watches, warnings and updated thoughts as we saw with the last few days weather situations can evolve rather quickly.

2. Thursday and Friday a low pressure weakens over the lakes with the boundary heading into TN. I’m going to keep an isolated shower or storm in the forecast for the boundary to the south and the far north being closer to the low. Highs will range from the mid to upper 70’s north to the low and mid 80’s south. not expecting any severe weather.

3. This boundary gets bumped northeast due to the heat ridge which is setting up shop for the summer in the southern plains, this will increase storm chances for the weekend with highs in the 80’s.  heavy rains will become a concern again. I suspect many outdoor plans could be in jeopardy.

cooler pattern in sight

June 19, 2011

1. No real changes for Monday/Tuesday. The boundary moves north with the chance of northern regions impacted by another morning MCS. Otherwise the heat ridge with hot and mostly sunny skies will dominate through Tuesday with lows near 70 and highs in the lower 90’s.

2. A stronger frontal boundary will move through Wednesday with more thunderstorms likely. shear and instability are both moderate in a warm moist airmass so the severe threat will be watched. highs will only be in the 80’s.