NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260226_0000
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)
=== ===== === ==== ==== === === === ====
Thu 02/26 00Z 0.52 2219  85  83  -7 0.00
Thu 02/26 01Z 0.50 2121  84  89  -6 0.00
Thu 02/26 02Z 0.59 2224  88  84  -6 0.02
Thu 02/26 03Z 0.64 2325  93  92  -6 0.03
Thu 02/26 04Z 0.82 2422  95  83  -7 0.02
Thu 02/26 05Z 1.39 2524  94  48  -8 0.01
Thu 02/26 06Z 1.78 2525  88  29  -9 0.01
Thu 02/26 07Z 1.99 2627  86  25 -10 0.00
Thu 02/26 08Z 1.99 2627  85  24 -12 0.00
Thu 02/26 09Z 1.76 2627  82  23 -12 0.00
Thu 02/26 10Z 2.10 2627  85  24 -13 0.00
Thu 02/26 11Z 1.82 2726  80  27 -14 0.00
Thu 02/26 12Z 1.36 2726  77  22 -14 0.00
Thu 02/26 13Z 1.28 2725  75  10 -14 0.00
Thu 02/26 14Z 1.56 2723  74   3 -14 0.00
Thu 02/26 15Z 3.90 2721  75   4 -14 0.00
Thu 02/26 16Z 7.82 2619  79   6 -14 0.00
Thu 02/26 17Z 9.61 2618  83   6 -14 0.00
Thu 02/26 18Z 8.46 2616  83   9 -14 0.00
Thu 02/26 19Z 7.01 2616  82  13 -13 0.00
Thu 02/26 20Z 4.88 2615  81  16 -13 0.00
Thu 02/26 21Z 3.32 2616  80  19 -13 0.00
Thu 02/26 22Z 1.19 2716  79  29 -13 0.00
Thu 02/26 23Z 0.88 2816  77  44 -13 0.00
Fri 02/27 00Z 0.83 2817  78  46 -13 0.00
Fri 02/27 01Z 0.75 2917  77  45 -13 0.00
Fri 02/27 02Z 0.64 2917  74  46 -13 0.00
Fri 02/27 03Z 0.54 2916  71  44 -13 0.00
Fri 02/27 04Z 0.46 2916  68  41 -13 0.00
Fri 02/27 05Z 0.39 2915  67  41 -12 0.00
Fri 02/27 06Z 0.35 2914  67  51 -12 0.00
Fri 02/27 08Z 0.32 2813  66  75 -12 0.00
Fri 02/27 09Z 0.33 2813  67  80 -12 0.00
Fri 02/27 10Z 0.33 2714  65  80 -11 0.00
Fri 02/27 11Z 0.34 2714  67  81 -11 0.00
Fri 02/27 12Z 0.36 2615  70  81 -11 0.00
Fri 02/27 13Z 0.39 2517  75  79 -11 0.00
Fri 02/27 14Z 0.43 2518  79  66 -10 0.00
Fri 02/27 16Z 0.51 2519  73  44  -9 0.00
Fri 02/27 17Z 0.53 2519  80  37  -8 0.00
Fri 02/27 18Z 0.58 2520  83  29  -7 0.00
Fri 02/27 19Z 0.63 2421  84  29  -7 0.00
Fri 02/27 20Z 0.68 2422  84  38  -7 0.00
Fri 02/27 21Z 0.68 2423  84  59  -6 0.00
Fri 02/27 22Z 0.64 2424  81  70  -4 0.00
Fri 02/27 23Z 0.61 2426  79  74  -3 0.00
Sat 02/28 00Z 0.62 2330  76  73  -2 0.00
Sat 02/28 01Z 0.62 2232  70  67  -2 0.00
Sat 02/28 02Z 0.63 2235  65  63  -1 0.00
Sat 02/28 03Z 0.64 2237  64  61  -1 0.00
Sat 02/28 04Z 0.64 2239  61  56   0 0.00
Sat 02/28 05Z 0.69 2242  58  54   0 0.00
Sat 02/28 06Z 0.71 2244  56  44   0 0.00
Sat 02/28 07Z 0.73 2246  52  53   0 0.00
Sat 02/28 08Z 0.76 2248  51  62   1 0.00
Sat 02/28 09Z 0.79 2347  58  62   0 0.00
Sat 02/28 10Z 0.79 2346  65  55   0 0.00
Sat 02/28 11Z 0.77 2344  69  56   0 0.00

Run total areal avg QPF for the 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