NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260510_0600
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)
=== ===== === ==== ==== === === === ====
Sun 05/10 06Z 0.41 2021  90  39   4 0.00
Sun 05/10 07Z 0.43 2122  94  50   4 0.00
Sun 05/10 08Z 0.59 2227  98  55   5 0.04
Sun 05/10 09Z 0.69 2324  98  91   4 0.03
Sun 05/10 10Z 0.71 2423  95  64   4 0.02
Sun 05/10 11Z 0.63 2420  95  49   4 0.01
Sun 05/10 12Z 0.51 2418  93  47   4 0.01
Sun 05/10 13Z 0.48 2317  92  58   5 0.00
Sun 05/10 14Z 0.52 2318  92  67   5 0.00
Sun 05/10 15Z 0.50 2316  91  79   5 0.00
Sun 05/10 16Z 0.57 2215  95  85   5 0.01
Sun 05/10 17Z 0.75 2412  98  88   4 0.02
Sun 05/10 18Z 0.48 2714  95  86   4 0.07
Sun 05/10 19Z 0.49 2820  84  89   4 0.04
Sun 05/10 20Z 0.61 2719  67  38   3 0.00
Sun 05/10 21Z 0.95 2819  69  44   2 0.00
Sun 05/10 22Z 0.94 2717  71  33   2 0.00
Sun 05/10 23Z 0.92 2717  73  47   2 0.00
Mon 05/11 00Z 1.11 2918  69  18   1 0.00
Mon 05/11 01Z 1.00 3020  64  22   0 0.00
Mon 05/11 02Z 0.93 3021  71  24   0 0.00
Mon 05/11 03Z 0.90 3020  79  22  -1 0.00
Mon 05/11 04Z 0.86 3019  80  21  -1 0.00
Mon 05/11 05Z 0.59 3118  84  19  -2 0.00
Mon 05/11 06Z 0.51 3116  85  17  -2 0.00
Mon 05/11 07Z 0.50 3115  84  17  -2 0.00
Mon 05/11 08Z 0.43 3114  86  14  -2 0.00
Mon 05/11 09Z 0.36 3112  86  17  -3 0.00
Mon 05/11 10Z 0.33 3110  85  18  -3 0.00
Mon 05/11 11Z 0.30 3009  84  24  -3 0.00
Mon 05/11 12Z 0.36 3008  84  23  -3 0.00
Mon 05/11 13Z 1.01 2808  84  29  -3 0.00
Mon 05/11 14Z 2.38 2808  82  31  -3 0.00
Mon 05/11 15Z 4.20 2708  73  31  -3 0.00
Mon 05/11 16Z 5.93 2709  72  35  -2 0.00
Mon 05/11 17Z 6.14 2610  74  47  -2 0.00
Mon 05/11 18Z 6.73 2711  68  62  -1 0.00
Mon 05/11 19Z 6.75 2711  64  69  -1 0.00
Mon 05/11 20Z 6.66 2811  63  74  -1 0.00
Mon 05/11 21Z 6.17 2811  62  71  -1 0.00
Mon 05/11 22Z 4.88 2911  64  69  -1 0.00
Mon 05/11 23Z 2.27 3011  67  69  -2 0.00
Tue 05/12 00Z 0.85 3112  73  69  -2 0.00
Tue 05/12 01Z 0.35 3213  80  67  -2 0.00
Tue 05/12 02Z 0.29 3214  78  68  -3 0.00
Tue 05/12 03Z 0.36 3217  81  73  -3 0.00
Tue 05/12 04Z 0.28 3318  82  66  -3 0.00
Tue 05/12 05Z 0.25 3319  82  61  -3 0.00
Tue 05/12 06Z 0.17 3320  75  53  -3 0.00
Tue 05/12 07Z 0.14 3420  71  42  -4 0.00
Tue 05/12 08Z 0.11 3419  68  22  -4 0.00
Tue 05/12 09Z 0.10 3418  67  18  -4 0.00
Tue 05/12 10Z 0.15 3317  66  23  -4 0.00
Tue 05/12 11Z 0.21 3316  67  34  -4 0.00
Tue 05/12 12Z 0.35 3215  68  41  -5 0.00
Tue 05/12 13Z 2.17 3214  71  46  -5 0.00
Tue 05/12 14Z 3.73 3113  71  45  -5 0.00
Tue 05/12 15Z 4.70 3112  69  38  -5 0.00
Tue 05/12 16Z 5.52 3011  69  27  -4 0.00
Tue 05/12 17Z 6.07 2911  70  32  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.25 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