Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 7:49 PM GMT on September 24, 2008
Invest 94L (Coastal Storm)...
(Courtesy of Penn State EWall)
My forecast has stayed pretty consistent the last couple of days with this complex scenerio. And so far I do not think I need to make any changes. The EURO model is still my model of choice as sort of an analog adding to my forecast. I was not sure if I was going to be able to create a new blog, but I decided that this was going to be a high impact event for late this week into the weekend. The sections below should take care of all forecasts and impacts for this event. A few things really excite me about this possibility because we are already beginning to potentially see where storm tracks may set up for the winter. Many people say it is too early for definite storm tracks to be patternized like those in September, but I think this may be a picture of what we may face down the road. Currently this storm is an Invest, 94L, and sitting off the Carolina's coastline moving westward towards inland. It is fighting some dry air and light shear, but still I cannot rule out a chance it develops into a tropical system or subtropical system. This sort of reminds me of Subtropical Storm Andrea which sat off the southeast coastline and caused lots of beach erosion and gusty winds. But this low pressure will move inland and cause areas of heavy rain also. I am looking at a storm track up the east coast as a trough pulls it north and then northeastward. Impacts with this storm I think will be quite similar to what many faced with Tropical Storm Hanna in terms of wind, rain, and wave action. Should be an interesting beach weekend with already surf being reported quite high near Ocean City, MD. Tight pressure gradient will also be felt as the high pressure pulls to the northeast in Northern New England currently. I hope to have people relay storm reports in this blog across the region and help to add to current forecast ideas. This blog is still under construction. Have a great day!!!
(Courtesy of NOAA)
This is going to be an extended period of high-impact weather coming late this week into the first half of the weekend with heavy rain, gusty winds, some severe weather, and coastal flooding. This will last from Thursday through Saturday night for effects on the Pennsylvania area. I decided not to make rain or wind maps for this storm, since I did not have the time today. But anyways here is my forecast for each of the impacts.
Heavy rain- Rainfall will be one of the primary threats from this event here in Pennsylvania. Now I have seen from the past that QPF is high overestimated across the Middle Atlantic during tropical events, so I am going to take a more reasonable forecast with a widespread 1-2inches for southcentral, to eastern, to northeastern Pennsylvania. There will be isolated higher amounts, but I am not anticipating any extended periods of very heavy rain. It should be a steady, moderate, stratiform type rainfall. Orographic lift may aid some rain totals in the Poconos and the southcentral mountains. Highest totals will be found along MD, DE, and NJ border counties.
Winds- Winds aloft will be quite strong, but they will have a hard time mixing down to the surface. Higher elevations of the southcentral Mountains, such as South Mountain will have some pretty strong winds with gusts near 45mph on the highest of the ridge tops. Laural highlands will also get gusty winds. Most valley locations will escape from the stronger winds. Now areas along the coastline will also see strong winds with gusts near 50mph, but not too much strong than that. With subtropical systems, the wind shield in not as compact as a purely tropical system.
Severe Weather- As with any system with somewhat tropical origins there is always the chance of an isolated tornado or wet downburst. We saw that this was the case with Hanna in Allentown, PA where an EF-1 unexpectedly touched down. Overall though I really do not anticipate any severe weather reports in the region, but I just wanted to highlight that the threat is there.
Storm Surge- A steady onshore flow for several days will result in consistent pushing of water over the beaches, especially during high tide. Waves will be in the general 5-10ft height during the height of the storm and a very higher waves will remain offshore. I think a 1-3ft water rise can be expected for areas along the Chesapeake. There will be less of a storm surge than there was with Hanna.
Overall this storm is less of a threat than Hanna was as there will be less severity of the impacts. This system is also subtropical, so the organization of the system is a little different. Typically the wind shield with subtropical systems is larger, but weaker. Also there usually is less of heavy rain rates with subtropical systems. So we will have to see what this storm does and if 93L has any impacts on the Northeast. Check back for more updates throughout the next couple of days.
"Radar for Central Pennsylvania"
"Radar for Eastern Pennsylvania"
Current Surface Map...
(Courtesy of Penn State EWall)
Current Weather Map...
A surge of high anomalies of moisture with PWATs near 2inches is quicking advancing north-northwest over the southeast and Middle Atlantic. Dewpoints will be on the rise along with a cirrus cloud deck overnight Wednesday night. As the subtropical low continues to linger off the North Carolina coastline, it will start to have winds turn easterly with a strong onshore flow for Thursday bringing in cooler temperatures with also a low LIFR stratus deck with ceilings as low as 500ft. High pressure will continue to move northeastward off towards to Canadian Maritimes, but a tight pressure gradient will develop. GFS 925mb charts indicate that winds aloft will near 45knots, but it does not look likely the most of those winds will mix down to the surface. Ridgetops though with elevations of 1500ft will feel some strong winds on Thursday and coastal areas may also see some strong winds. Moisture will continue to funnel in off the Atlantic and several shields of rainfall will develop varying slightly in intensity. The center of the low will begin to pull to the north and then northeastward as a cold front approaches from the west with another trough. The front will be very slow moving. For Friday the low pressure should be over the Tidewaters of Virginia causing the heaviest rainfall to fall to the northwest of the center which will be right along the area just east of the Appalachians and sort of close to the I-95 corridor. Winds will remain easterly, but begin to calm down throughout the day. Low stratus may keep a hold on the temperatures with them possibily in the 50s for highs on Friday. The heaviest time period for rain will be Friday night and then by Saturday the rain begins to die out, but low stratus will remain over the region. This entire storm system will be very similar to typical coastal lows in months such as late April and May. Some of the other sections in this blog will contain more details on the impacts. But above is the general setup.
Current Water Vapor Loop...
(Courtesy of Penn State EWall)
Computer model forecasts...
Looking at the computer models I still feel the EURO has the best feel for this storm with location and strength of the low pressure system. The NAM also seemed to forecast this system pretty well, but slightly too strong when coming ashore. GFS seems to be suffering from some major convective feedback errors with just blotches of high QPF all over the map. I like the HPC rainfall map as it incorporates the orographic lifting mechanism for parts of southcentral Pennsylvania.
SREF model also seems to have a good hold on precipitation totals, possibly a little too far west though on some of the high QPF. This has been quite a complex scenerio so I would not be surprised to see a few surprises along the way with this storm. Looks like highest rainfall totals will be in counties such as Adams, Franklin, York, Lancaster, Chester, Delaware, Philadelphia, Bucks, and Montgomery. Franklin and Adams Counties will get some of that extra orographic lift added to their precipitation totals. I would not be surprised to see an isolated 4inch rainfall total reported. A concern of mine though right now is that the precipitation shield is pretty small right now near the subtropical low, but it is expanding, so I guess we will have to wait and see. Looking at the model soundings from the GFS it prints out a max rainfall total of nearly 4inches at Philadelphia International Airport... Link. I think though some of that total is due to the convective feedback errors the model is suffering.
Looking ahead towards late this weekend, I am looking like I will not have the time to get another blog out until next Tuesday. So this final thoughts section will cover the forecasts from Sunday through Tuesday and beyond into the long term. From busy period again starting early next week as a very strong cold front works into the region behind this coastal storm. High pressure moves over the region for Monday bringing once again cooler than normal temperatures along with dry humidity levels. Another cold front quickly approaches for Tuesday with a very, very deep and amplified trough over much of the Midwest and Northeast with some of the coolest weather of the season. Models have been back and forth with solutions from a Appalachian runner type storm system with heavy rain, or another east coast coastal storm. This reminds me of a winter time type scenerio. This storm system may impact midweek. The deep trough will cause some very low isothermal layers with possibily the 0C line as far south as Pennsylvania. After high pressure moves over the region after what ever storm system forms, then we could see some widespread killing frosts over the region. I still am holding to my forecast of an early October frost or freeze widespread over Pennsylvania. NAO levels remain towards negative and very high PNA levels remain over the western Rockies with a anomalious large ridge with warmer than normal temperatures. Global models like the GFS and EURO have been forecasting this scenerio for quite a while now. So overall the long term pattern looks quite unsettled and cool. Also I just want to lastly mention, I cannot rule out a few snowflakes across far Northern England during this time period as upper levels and lower levels support ice crystal growth down to elevations of 4,000ft. So very interesting period is ahead. Winter is coming for those of you who do not want to admit it, lol. Have a great day!!!
Forecast Model Links
-NAM model 12z...Link
-GFS model 12z...Link
-NMM model 12z...Link
-SREF model 9z...Link
Severe Weather Links
-Atmospheric Soundings Skewt T charts...Link
-SPC Mesoscale Analysis Pages...Link
-Public Spotter Reports for State College NWS...Link
-Severe Weather Model Forecast indices...Link
-Severe Weather Parameter Definitions...Link
-Automated Pennsylvania Rainfall Recording Stations...Link
-Flash Flooding Guidance...Link
-HPC Forecasts for Excessive Rainfall...Link
-Hydrology Predictions for Lakes, Rivers, and Streams...Link
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