Here are my (not-so) quick tips for picking a target area the the night before. After doing an
upper air analysis (with
WV and IR sat imagery,
RAOBs,
VWPs, ) and looking at mid-upper atmosphere model discrepancies for the target period I use the
COD regional views and draw each of the features (that I list below) from the GFS, WRF, RUC, SREF and sometimes the Euro and Ukie onto my
white board with US overlay. Skip Talbot has framed
all of the models on his website from all of the major sources, and it makes for very easy navigation. Using these inputs I then draw the 'consensus' line which will lean towards 1) what I gathered from my upper-air analysis 2) whichever model is more in line with the RUC at 12 hrs and even more influential- 3) whichever model has been performing better as of late.
The target should be refined in the morning using 12z
RAOBs and model runs and should continue to be refined throughout the day based on analysis of
vis sat,
surface obs,
SPC Mesoanalysis,
radar (look for boundaries) and RUC updates (
UCAR is quicker than
COD with the updates, but COD has 'zoomed-in' regional views).
Note: You should have an idea of initiation time (step 6) before beginning the FCST map.
SPC's SREF precip data are very helpful here, especially the
Spaghetti 3hr convective pcpn > .01in map. Use the initiation time you deduce as your FCST time and complete all the steps (layers) for that specific time. If your initiation time is between model output times, 22z for example, you will have to make educated adjustments to the data (extrapolate the 18z data to 22z with the 00z data in mind).
1)
Surface features- Draw the consensus surface low and notate the estimated strength (in mb). Draw the consensus boundaries (warm front, cold front and dry line).
2)
Moisture- Narrow down the target area by drawing the consensus
60 degree isodrotherm. This should be within the warm sector drawn in the first step. Unless the max temps are in the 60's or low 70's, you'll be hard pressed to get a good storm below 60 td. Draw the 65 isodrotherm lightly if it is in or near the general target area.
3)
Instability- The cut-off number for the area of delineation will change with the seasons and differ between systems, but a good number to use as a minimum for tornadoes is
1000 j/kg of MLCAPE. Draw a 2000 j/kg (or the next 1000 higher than the first line) line lightly if available.
4)
Lift- Draw your lift line directly on the warm front and cold front, or dryline if there is one. This is where you should look at
fcst soundings for your general target area along with
fcst CINH. Place dots on your map where the sounding are and notate next to them how strong the CAP is progged to be (I use 1 through 10 with 10 being nuclear CAP). Take the line out into the warm sector as far as you think the CAP could be overcome (consider the current/overnight convection and where OFB's may be) and connect to the other line.
5)
Shear- Start by drawing consensus 500mb wind barbs over a few locations in the target area, preferably near the fcst sounding locations. Then draw the consensus 850mb wind barbs and sfc wind barbs for the same locations. Draw FCST hodograph for extra credit
The best shear areas will be subjective and change throughout the day, but try to circle the area within your warm sector where the best shear (speed
and directional!) will be at the time of initiation. Which brings me to..
6)
Precip- Take into account the
WRF,
GFS, and
SREF forecast precip maps while considering a) how the CAP strength will change through the day and b) how the boundaries will move [ie retreating dryline, screaming cold front]. I have been very impressed with the performance of the NSSL's
4.0 km experimental WRF precip maps and simulated reflexivity. Delineate the areas where you think precip will break out while placing an emphasis on the areas where the likely storm mode will be supercellular.
7)
Eye-candy models- Getting close to the end here so your FCST map should look like a hot mess. This is when I look at some of Earl's severe parameters like EHI, Sig Tor and Sup Composite. Skip Talbot has these models framed
HERE at the top for easy navigation. I don't delineate an area for these because they are each dependant on the particular model, but I do factor these somewhat into my final target forecast.
This is where you take all of the factors above into account and draw your target area. I like to start off with a relatively large area where I think tornadoes are possible. Then I narrow down my target area and draw where I think tornadoes will be likely and then narrow that down further by placing a dot on the map as my target county. I then erase all of the lines and notes on the map except for the sfc low, sfc boundaries and target area. I don't look at the SPC's Day 1 before finishing because I think it makes me a better forecaster. This is what my finished product looks like:
