Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260120_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 01/20 18Z 5.96 2514 81 66 -20 0.00
Tue 01/20 19Z 7.67 2618 83 66 -20 0.00
Tue 01/20 20Z 8.43 2621 82 66 -20 0.01
Tue 01/20 21Z 6.91 2622 77 62 -20 0.01
Tue 01/20 22Z 5.03 2623 78 51 -20 0.00
Tue 01/20 23Z 2.47 2625 78 44 -21 0.00
Wed 01/21 00Z 1.83 2627 75 39 -20 0.00
Wed 01/21 01Z 1.41 2629 70 38 -20 0.00
Wed 01/21 02Z 1.27 2630 72 39 -20 0.00
Wed 01/21 03Z 1.10 2629 76 43 -20 0.00
Wed 01/21 04Z 1.01 2629 77 41 -19 0.00
Wed 01/21 05Z 1.00 2629 81 40 -19 0.00
Wed 01/21 06Z 0.91 2528 84 39 -19 0.00
Wed 01/21 07Z 0.88 2529 82 35 -19 0.00
Wed 01/21 08Z 0.84 2529 78 22 -18 0.00
Wed 01/21 09Z 0.81 2530 78 14 -18 0.00
Wed 01/21 10Z 0.72 2528 76 9 -17 0.00
Wed 01/21 11Z 0.70 2528 74 9 -17 0.00
Wed 01/21 12Z 0.64 2527 71 9 -17 0.00
Wed 01/21 13Z 0.57 2526 65 9 -16 0.00
Wed 01/21 14Z 0.56 2525 61 12 -16 0.00
Wed 01/21 15Z 0.53 2424 57 33 -15 0.00
Wed 01/21 16Z 0.49 2422 55 65 -15 0.00
Wed 01/21 17Z 0.43 2320 51 87 -14 0.00
Wed 01/21 18Z 0.40 2220 46 91 -14 0.00
Wed 01/21 19Z 0.39 2122 41 87 -13 0.00
Wed 01/21 20Z 0.36 2122 54 85 -13 0.00
Wed 01/21 21Z 0.27 2025 69 89 -12 0.00
Wed 01/21 22Z 0.21 1928 80 88 -11 0.00
Wed 01/21 23Z 0.20 1932 88 88 -11 0.02
Thu 01/22 00Z 0.33 2037 90 89 -12 0.04
Thu 01/22 01Z 0.51 2041 91 89 -12 0.03
Thu 01/22 02Z 0.57 2141 92 87 -10 0.01
Thu 01/22 03Z 0.62 2239 93 88 -9 0.01
Thu 01/22 04Z 0.66 2236 93 91 -9 0.01
Thu 01/22 05Z 0.67 2334 94 82 -8 0.01
Thu 01/22 06Z 0.68 2333 93 67 -8 0.01
Thu 01/22 07Z 0.69 2331 92 54 -8 0.00
Thu 01/22 08Z 0.68 2330 93 45 -8 0.00
Thu 01/22 09Z 0.67 2328 93 43 -9 0.00
Thu 01/22 10Z 0.66 2327 93 49 -9 0.00
Thu 01/22 11Z 0.68 2327 94 59 -9 0.00
Thu 01/22 12Z 0.74 2328 94 72 -9 0.00
Thu 01/22 13Z 0.80 2329 94 81 -9 0.01
Thu 01/22 14Z 0.84 2330 92 74 -9 0.01
Thu 01/22 15Z 1.00 2331 94 71 -9 0.01
Thu 01/22 16Z 1.33 2431 91 60 -10 0.01
Thu 01/22 17Z 1.67 2427 89 49 -10 0.00
Thu 01/22 18Z 3.47 2426 92 60 -10 0.00
Thu 01/22 19Z 5.05 2426 92 44 -10 0.01
Thu 01/22 20Z 4.07 2428 89 44 -10 0.01
Thu 01/22 21Z 5.90 2431 85 40 -11 0.01
Thu 01/22 22Z 4.07 2432 85 45 -11 0.00
Thu 01/22 23Z 4.13 2434 88 46 -12 0.00
Fri 01/23 00Z 3.30 2534 89 43 -13 0.01
Fri 01/23 01Z 2.98 2533 87 38 -14 0.01
Fri 01/23 02Z 1.98 2533 82 33 -14 0.00
Fri 01/23 03Z 1.69 2533 82 33 -15 0.00
Fri 01/23 04Z 2.00 2631 83 32 -16 0.00
Fri 01/23 05Z 1.78 2629 84 31 -17 0.00
Run total areal avg QPF for the greens is: 0.25 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1