NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260328_0600
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)
=== ===== === ==== ==== === === === ====
Sat 03/28 06Z 0.32 3213  81  15 -15 0.00
Sat 03/28 07Z 0.44 3214  81  26 -16 0.00
Sat 03/28 08Z 0.48 3214  80  26 -16 0.00
Sat 03/28 09Z 0.56 3213  81  45 -17 0.00
Sat 03/28 10Z 0.65 3114  83  53 -17 0.00
Sat 03/28 11Z 0.59 3114  84  59 -17 0.00
Sat 03/28 12Z 0.60 3112  84  63 -17 0.00
Sat 03/28 13Z 1.28 3110  82  61 -17 0.00
Sat 03/28 14Z 2.12 3009  77  63 -17 0.00
Sat 03/28 15Z 2.82 2909  71  63 -16 0.00
Sat 03/28 16Z 4.16 2809  67  61 -16 0.00
Sat 03/28 17Z 6.64 2710  68  66 -15 0.00
Sat 03/28 18Z 8.48 2612  70  70 -14 0.00
Sat 03/28 19Z 8.56 2615  74  74 -14 0.00
Sat 03/28 20Z 6.20 2717  80  69 -14 0.00
Sat 03/28 21Z 8.68 2718  74  59 -14 0.00
Sat 03/28 22Z 6.86 2819  76  57 -14 0.01
Sat 03/28 23Z 3.39 2820  81  59 -14 0.00
Sun 03/29 00Z 4.21 2824  83  57 -14 0.01
Sun 03/29 01Z 3.92 2825  80  44 -15 0.00
Sun 03/29 02Z 2.04 2823  74  27 -14 0.00
Sun 03/29 03Z 1.97 2823  71  14 -14 0.00
Sun 03/29 04Z 2.01 2824  75  20 -14 0.00
Sun 03/29 05Z 2.02 2825  81  48 -14 0.00
Sun 03/29 06Z 1.79 2823  85  67 -14 0.00
Sun 03/29 07Z 1.67 2823  89  71 -14 0.00
Sun 03/29 08Z 1.33 2822  90  77 -14 0.00
Sun 03/29 09Z 1.18 2822  91  76 -14 0.00
Sun 03/29 10Z 1.02 2722  93  76 -13 0.00
Sun 03/29 11Z 0.87 2720  93  73 -13 0.00
Sun 03/29 12Z 0.82 2621  92  77 -12 0.00
Sun 03/29 13Z 0.77 2521  89  80 -11 0.00
Sun 03/29 14Z 0.80 2521  87  79 -10 0.00
Sun 03/29 15Z 0.94 2519  81  81 -10 0.00
Sun 03/29 16Z 1.03 2418  68  86  -9 0.00
Sun 03/29 17Z 2.15 2319  62  89  -8 0.00
Sun 03/29 18Z 2.65 2220  60  80  -8 0.00
Sun 03/29 19Z 2.80 2222  58  78  -7 0.00
Sun 03/29 20Z 2.90 2323  58  64  -6 0.00
Sun 03/29 21Z 1.56 2325  59  73  -5 0.00
Sun 03/29 22Z 1.34 2427  60  45  -5 0.00
Sun 03/29 23Z 1.48 2429  60  31  -4 0.00
Mon 03/30 00Z 1.55 2430  58  12  -4 0.00
Mon 03/30 01Z 1.45 2531  57   7  -3 0.00
Mon 03/30 02Z 1.55 2532  56   9  -3 0.00
Mon 03/30 03Z 1.58 2532  59  14  -3 0.00
Mon 03/30 04Z 1.29 2530  57  38  -2 0.00
Mon 03/30 05Z 1.17 2529  59  69  -2 0.00
Mon 03/30 06Z 1.26 2527  68  81  -2 0.00
Mon 03/30 07Z 0.96 2525  72  85  -2 0.00
Mon 03/30 08Z 0.78 2424  74  71  -2 0.01
Mon 03/30 09Z 0.85 2424  76  68  -2 0.00
Mon 03/30 10Z 0.90 2525  81  77  -2 0.00
Mon 03/30 11Z 0.88 2524  80  88  -2 0.00
Mon 03/30 12Z 0.90 2524  76  92  -2 0.00
Mon 03/30 13Z 0.91 2524  80  89  -2 0.00
Mon 03/30 14Z 0.87 2524  78  77  -2 0.00
Mon 03/30 15Z 0.86 2523  67  81   0 0.00
Mon 03/30 16Z 0.94 2524  67  86   0 0.00
Mon 03/30 17Z 1.08 2424  68  81   0 0.00

Run total areal avg QPF for the greens is: 0.03 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