NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260328_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)
=== ===== === ==== ==== === === === ====
Sat 03/28 12Z 0.32 3009  83  55 -16 0.00
Sat 03/28 13Z 0.71 2910  82  68 -16 0.00
Sat 03/28 14Z 2.37 2909  82  62 -16 0.00
Sat 03/28 15Z 4.39 2909  77  58 -16 0.00
Sat 03/28 16Z 5.40 2809  68  64 -15 0.00
Sat 03/28 17Z 6.10 2809  65  65 -14 0.00
Sat 03/28 18Z 6.67 2610  68  73 -13 0.00
Sat 03/28 19Z 5.69 2514  78  78 -13 0.00
Sat 03/28 20Z 7.58 2717  78  78 -13 0.01
Sat 03/28 21Z 10.27 2719  69  62 -13 0.01
Sat 03/28 22Z 9.41 2720  74  53 -13 0.00
Sat 03/28 23Z 4.85 2722  80  53 -13 0.00
Sun 03/29 00Z 2.89 2723  85  48 -14 0.00
Sun 03/29 01Z 4.61 2824  80  36 -14 0.00
Sun 03/29 02Z 5.58 2825  78  24 -14 0.00
Sun 03/29 03Z 2.22 2824  74  13 -14 0.00
Sun 03/29 04Z 1.59 2823  70  20 -14 0.00
Sun 03/29 05Z 1.38 2822  75  52 -14 0.00
Sun 03/29 06Z 1.43 2822  83  80 -14 0.00
Sun 03/29 07Z 1.28 2822  86  77 -14 0.00
Sun 03/29 08Z 1.05 2823  86  74 -13 0.00
Sun 03/29 09Z 1.02 2822  89  80 -13 0.00
Sun 03/29 10Z 0.94 2722  92  80 -13 0.00
Sun 03/29 11Z 0.88 2722  92  80 -12 0.00
Sun 03/29 12Z 0.75 2721  86  76 -11 0.00
Sun 03/29 13Z 0.76 2621  83  70 -11 0.00
Sun 03/29 14Z 0.88 2621  85  77 -10 0.00
Sun 03/29 15Z 0.96 2619  79  70  -9 0.00
Sun 03/29 16Z 1.04 2617  70  68  -9 0.00
Sun 03/29 17Z 1.50 2416  64  75  -8 0.00
Sun 03/29 18Z 3.38 2318  60  74  -8 0.00
Sun 03/29 19Z 8.72 2319  58  72  -7 0.00
Sun 03/29 20Z 7.22 2320  57  55  -7 0.00
Sun 03/29 21Z 2.06 2322  58  36  -6 0.00
Sun 03/29 22Z 1.26 2424  62  27  -5 0.00
Sun 03/29 23Z 1.23 2426  65  26  -4 0.00
Mon 03/30 00Z 1.30 2426  65   9  -4 0.00
Mon 03/30 01Z 1.27 2526  62  12  -3 0.00
Mon 03/30 02Z 1.23 2527  59   6  -3 0.00
Mon 03/30 03Z 1.25 2527  58   3  -2 0.00
Mon 03/30 04Z 1.18 2427  59  14  -2 0.00
Mon 03/30 05Z 1.04 2427  61  34  -2 0.00
Mon 03/30 06Z 0.97 2428  65  66  -1 0.00
Mon 03/30 07Z 0.86 2427  67  81  -1 0.00
Mon 03/30 08Z 0.80 2426  73  52  -1 0.00
Mon 03/30 09Z 0.73 2425  76  74   0 0.00
Mon 03/30 10Z 0.66 2424  76  69   0 0.00
Mon 03/30 11Z 0.75 2427  81  62  -1 0.00
Mon 03/30 12Z 0.86 2529  90  36  -1 0.00
Mon 03/30 13Z 0.85 2529  90  62  -1 0.00
Mon 03/30 14Z 0.84 2529  93  74  -1 0.01
Mon 03/30 15Z 0.87 2529  89  75   0 0.00
Mon 03/30 16Z 0.86 2628  80  80   0 0.00
Mon 03/30 17Z 0.86 2627  79  67   0 0.00
Mon 03/30 18Z 0.90 2625  78  65   1 0.00
Mon 03/30 19Z 0.99 2524  80  58   1 0.00
Mon 03/30 20Z 1.29 2524  84  56   1 0.00
Mon 03/30 21Z 1.44 2425  85  56   1 0.00
Mon 03/30 22Z 1.38 2427  86  58   1 0.00
Mon 03/30 23Z 1.28 2527  85  57   2 0.00

Run total areal avg QPF for the Central_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