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Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260630_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 06/30 12Z 0.37 2311 56 52 15 0.00
Tue 06/30 13Z 0.42 2311 54 48 15 0.00
Tue 06/30 14Z 0.42 2211 54 47 15 0.00
Tue 06/30 15Z 0.47 2210 55 41 16 0.00
Tue 06/30 16Z 1.08 2208 55 42 16 0.00
Tue 06/30 17Z 1.91 2209 56 53 16 0.00
Tue 06/30 18Z 1.74 2109 58 59 16 0.00
Tue 06/30 19Z 1.87 2110 62 64 17 0.00
Tue 06/30 20Z 2.27 2214 79 81 16 0.00
Tue 06/30 21Z 0.42 2313 86 82 16 0.01
Tue 06/30 22Z 0.46 2515 78 85 17 0.00
Tue 06/30 23Z 0.60 2618 83 83 16 0.00
Wed 07/01 00Z 0.61 2718 84 80 16 0.00
Wed 07/01 01Z 0.70 2620 83 78 17 0.00
Wed 07/01 02Z 0.66 2620 86 67 17 0.00
Wed 07/01 03Z 0.65 2519 90 62 17 0.00
Wed 07/01 04Z 0.56 2418 95 63 17 0.01
Wed 07/01 05Z 0.58 2418 96 52 17 0.01
Wed 07/01 08Z 0.64 2620 96 40 17 0.02
Wed 07/01 10Z 0.67 2622 97 29 18 0.02
Wed 07/01 11Z 0.69 2623 95 32 18 0.02
Wed 07/01 12Z 0.66 2623 94 42 19 0.02
Wed 07/01 13Z 0.58 2620 95 51 18 0.04
Wed 07/01 14Z 0.48 2716 94 65 19 0.05
Wed 07/01 15Z 0.36 2712 93 71 19 0.06
Wed 07/01 16Z 0.42 2613 95 68 19 0.06
Wed 07/01 17Z 0.37 2612 87 70 19 0.09
Wed 07/01 18Z 0.40 2612 88 71 20 0.14
Wed 07/01 19Z 0.41 2512 87 72 19 0.05
Wed 07/01 20Z 0.33 2710 79 66 20 0.13
Wed 07/01 21Z 0.51 2615 74 68 20 0.08
Wed 07/01 22Z 0.53 2618 75 52 21 0.24
Wed 07/01 23Z 0.59 2620 74 44 21 0.40
Thu 07/02 00Z 0.61 2823 73 46 21 0.02
Thu 07/02 01Z 0.66 2626 84 51 20 0.08
Thu 07/02 02Z 0.68 2625 70 57 21 0.01
Thu 07/02 03Z 0.60 2724 77 58 21 0.00
Thu 07/02 04Z 0.57 2824 81 42 20 0.01
Thu 07/02 05Z 0.56 2822 85 28 19 0.00
Thu 07/02 06Z 0.49 2821 86 28 19 0.00
Thu 07/02 07Z 0.45 2920 88 36 19 0.00
Thu 07/02 08Z 0.38 3019 85 27 19 0.00
Thu 07/02 09Z 0.35 3019 81 6 20 0.00
Thu 07/02 10Z 0.31 3019 73 3 20 0.00
Thu 07/02 11Z 0.30 3018 63 8 20 0.00
Thu 07/02 12Z 0.33 2918 46 7 21 0.00
Thu 07/02 13Z 0.29 3016 37 18 21 0.01
Thu 07/02 14Z 0.31 2915 36 27 22 0.01
Thu 07/02 15Z 0.31 2813 37 33 22 0.00
Thu 07/02 16Z 0.34 2813 52 28 22 0.00
Thu 07/02 17Z 0.38 2713 67 25 21 0.00
Thu 07/02 18Z 0.47 2713 67 27 21 0.00
Thu 07/02 19Z 0.77 2416 85 33 20 0.00
Thu 07/02 20Z 0.89 2518 88 44 20 0.00
Thu 07/02 21Z 1.04 2521 86 50 20 0.00
Thu 07/02 22Z 1.08 2523 81 48 20 0.00
Thu 07/02 23Z 1.27 2524 80 60 20 0.09
Run total areal avg QPF for the Central_Greens is: 1.68 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