NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260226_0000
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)
=== ===== === ==== ==== === === === ====
Thu 02/26 00Z 0.57 2119  83  81  -7 0.00
Thu 02/26 01Z 0.57 2122  81  85  -6 0.00
Thu 02/26 02Z 0.73 2226  85  83  -6 0.01
Thu 02/26 03Z 0.75 2326  93  92  -5 0.02
Thu 02/26 04Z 0.84 2522  95  84  -7 0.03
Thu 02/26 05Z 1.33 2623  94  42  -8 0.01
Thu 02/26 06Z 1.68 2625  92  25  -9 0.01
Thu 02/26 07Z 1.82 2626  87  31 -10 0.01
Thu 02/26 08Z 2.16 2627  82  17 -11 0.00
Thu 02/26 09Z 1.98 2627  79  15 -12 0.00
Thu 02/26 10Z 2.41 2628  80  16 -13 0.00
Thu 02/26 11Z 2.04 2727  75  24 -14 0.00
Thu 02/26 12Z 1.35 2727  69   8 -14 0.00
Thu 02/26 13Z 1.24 2726  66   1 -14 0.00
Thu 02/26 14Z 1.54 2724  66   2 -14 0.00
Thu 02/26 15Z 4.93 2722  69   4 -14 0.00
Thu 02/26 16Z 9.76 2619  74   5 -14 0.00
Thu 02/26 17Z 12.15 2618  79   6 -13 0.00
Thu 02/26 18Z 10.60 2617  80   9 -13 0.00
Thu 02/26 19Z 8.55 2616  80  15 -13 0.00
Thu 02/26 20Z 6.24 2615  79  18 -12 0.00
Thu 02/26 21Z 4.44 2616  77  21 -12 0.00
Thu 02/26 22Z 1.31 2715  77  28 -12 0.00
Thu 02/26 23Z 0.88 2815  76  44 -12 0.00
Fri 02/27 00Z 0.78 2915  76  51 -12 0.00
Fri 02/27 01Z 0.66 2915  75  48 -12 0.00
Fri 02/27 02Z 0.52 2915  72  46 -12 0.00
Fri 02/27 03Z 0.42 2915  66  44 -12 0.00
Fri 02/27 04Z 0.34 2915  61  38 -12 0.00
Fri 02/27 05Z 0.29 2914  59  35 -11 0.00
Fri 02/27 06Z 0.27 2913  58  43 -11 0.00
Fri 02/27 08Z 0.26 2813  56  70 -11 0.00
Fri 02/27 09Z 0.28 2813  58  78 -11 0.00
Fri 02/27 10Z 0.28 2814  57  79 -10 0.00
Fri 02/27 11Z 0.31 2714  59  80 -10 0.00
Fri 02/27 12Z 0.35 2616  63  79 -10 0.00
Fri 02/27 13Z 0.39 2618  72  77  -9 0.00
Fri 02/27 14Z 0.43 2519  77  66  -9 0.00
Fri 02/27 16Z 0.55 2521  67  44  -8 0.00
Fri 02/27 17Z 0.58 2522  77  37  -7 0.00
Fri 02/27 18Z 0.63 2522  81  28  -7 0.00
Fri 02/27 19Z 0.69 2522  81  29  -6 0.00
Fri 02/27 20Z 0.75 2522  81  42  -6 0.00
Fri 02/27 21Z 0.72 2423  80  53  -5 0.00
Fri 02/27 22Z 0.66 2424  78  63  -4 0.00
Fri 02/27 23Z 0.67 2427  77  69  -3 0.00
Sat 02/28 00Z 0.71 2329  74  67  -3 0.00
Sat 02/28 01Z 0.71 2331  69  62  -2 0.00
Sat 02/28 02Z 0.71 2233  64  59  -1 0.00
Sat 02/28 03Z 0.74 2235  64  56  -1 0.00
Sat 02/28 04Z 0.73 2237  61  52  -1 0.00
Sat 02/28 05Z 0.79 2240  58  48   0 0.00
Sat 02/28 06Z 0.82 2244  55  44   0 0.00
Sat 02/28 07Z 0.84 2246  49  44   0 0.00
Sat 02/28 08Z 0.86 2248  48  50   1 0.00
Sat 02/28 09Z 0.86 2348  52  57   1 0.00
Sat 02/28 10Z 0.84 2346  59  51   1 0.00
Sat 02/28 11Z 0.82 2344  63  51   1 0.00

Run total areal avg QPF for the Central_Greens is: 0.09 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