Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260119_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)
=== ===== === ==== ==== === === === ====
Mon 01/19 12Z 0.31 2408  89  65 -14 0.00
Mon 01/19 13Z 0.41 2410  91  63 -14 0.00
Mon 01/19 14Z 0.59 2313  91  66 -14 0.00
Mon 01/19 15Z 0.61 2313  86  74 -14 0.00
Mon 01/19 16Z 0.96 2315  83  67 -14 0.00
Mon 01/19 17Z 3.74 2316  81  64 -15 0.00
Mon 01/19 18Z 5.68 2317  79  72 -15 0.00
Mon 01/19 19Z 2.73 2317  83  78 -14 0.00
Mon 01/19 20Z 5.06 2319  87  79 -15 0.00
Mon 01/19 21Z 1.91 2323  90  73 -14 0.00
Mon 01/19 22Z 2.26 2426  89  65 -14 0.01
Mon 01/19 23Z 1.98 2426  89  45 -14 0.00
Tue 01/20 00Z 1.95 2427  85  36 -15 0.00
Tue 01/20 01Z 1.93 2429  79  40 -15 0.00
Tue 01/20 02Z 2.61 2431  86  55 -15 0.00
Tue 01/20 03Z 7.75 2432  78  51 -16 0.00
Tue 01/20 04Z 3.11 2431  77  46 -17 0.00
Tue 01/20 05Z 1.84 2430  78  48 -17 0.00
Tue 01/20 06Z 1.72 2533  85  50 -17 0.00
Tue 01/20 07Z 1.32 2631  84  50 -17 0.00
Tue 01/20 08Z 1.19 2629  85  48 -17 0.00
Tue 01/20 09Z 1.37 2628  88  44 -18 0.00
Tue 01/20 10Z 1.72 2627  90  42 -18 0.00
Tue 01/20 11Z 2.57 2626  88  39 -19 0.00
Tue 01/20 12Z 2.91 2625  82  38 -20 0.00
Tue 01/20 13Z 2.63 2724  79  40 -20 0.01
Tue 01/20 14Z 4.77 2722  78  43 -21 0.00
Tue 01/20 15Z 7.54 2719  78  49 -21 0.00
Tue 01/20 16Z 9.89 2618  78  61 -21 0.00
Tue 01/20 17Z 11.26 2617  78  66 -21 0.00
Tue 01/20 18Z 11.42 2518  79  67 -21 0.00
Tue 01/20 19Z 11.17 2519  79  65 -21 0.00
Tue 01/20 20Z 12.43 2521  73  68 -20 0.00
Tue 01/20 21Z 10.66 2622  74  59 -21 0.00
Tue 01/20 22Z 6.67 2623  76  47 -21 0.00
Tue 01/20 23Z 4.87 2624  79  48 -21 0.00
Wed 01/21 00Z 3.50 2626  76  49 -21 0.00
Wed 01/21 01Z 2.45 2628  78  47 -21 0.00
Wed 01/21 02Z 1.69 2629  79  45 -21 0.00
Wed 01/21 03Z 1.29 2728  78  46 -21 0.00
Wed 01/21 04Z 1.13 2627  81  46 -20 0.00
Wed 01/21 05Z 1.01 2728  82  45 -20 0.00
Wed 01/21 06Z 0.96 2728  83  45 -20 0.00
Wed 01/21 07Z 0.85 2626  84  41 -20 0.00
Wed 01/21 08Z 0.76 2625  84  35 -19 0.00
Wed 01/21 09Z 0.83 2527  86  22 -19 0.00
Wed 01/21 10Z 0.72 2527  77  11 -18 0.00
Wed 01/21 11Z 0.64 2527  65  11 -17 0.00
Wed 01/21 12Z 0.64 2528  60  11 -16 0.00
Wed 01/21 13Z 0.62 2528  55  15 -15 0.00
Wed 01/21 14Z 0.59 2527  51  26 -14 0.00
Wed 01/21 15Z 0.49 2523  47  30 -14 0.00
Wed 01/21 16Z 0.44 2321  46  90 -13 0.00
Wed 01/21 17Z 0.40 2221  42  88 -13 0.00
Wed 01/21 18Z 0.40 2122  36  92 -13 0.00
Wed 01/21 19Z 0.45 2026  36  91 -13 0.00
Wed 01/21 20Z 0.39 2027  49  86 -11 0.00
Wed 01/21 21Z 0.32 1928  41  74 -10 0.00
Wed 01/21 22Z 0.32 1932  40  83  -9 0.00
Wed 01/21 23Z 0.35 1936  38  89  -8 0.00

Run total areal avg QPF for the Central_Greens is: 0.02 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