Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260122_0000
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)
=== ===== === ==== ==== === === === ====
Thu 01/22 00Z 0.44 2033  82  87 -11 0.00
Thu 01/22 01Z 0.63 2038  77  80 -11 0.00
Thu 01/22 02Z 0.72 2139  80  90 -10 0.00
Thu 01/22 03Z 0.75 2139  86  93  -9 0.00
Thu 01/22 04Z 0.72 2237  91  95  -8 0.01
Thu 01/22 05Z 0.72 2236  94  96  -8 0.02
Thu 01/22 06Z 0.72 2236  94  95  -7 0.02
Thu 01/22 07Z 0.75 2236  93  94  -7 0.02
Thu 01/22 08Z 0.77 2236  93  80  -6 0.02
Thu 01/22 09Z 0.80 2335  94  48  -6 0.02
Thu 01/22 10Z 0.86 2335  93  78  -6 0.01
Thu 01/22 11Z 0.95 2432  91  91  -7 0.01
Thu 01/22 12Z 1.10 2431  92  88  -9 0.01
Thu 01/22 13Z 1.24 2432  91  73  -9 0.00
Thu 01/22 14Z 1.27 2531  86  60  -9 0.00
Thu 01/22 15Z 1.41 2530  87  71 -10 0.00
Thu 01/22 16Z 1.67 2528  91  85 -10 0.00
Thu 01/22 17Z 3.40 2525  87  68 -11 0.00
Thu 01/22 18Z 4.32 2526  86  53 -11 0.00
Thu 01/22 19Z 7.66 2527  89  25 -11 0.00
Thu 01/22 20Z 10.35 2529  87  13 -11 0.00
Thu 01/22 21Z 9.26 2531  86  24 -12 0.00
Thu 01/22 22Z 5.32 2632  80  26 -13 0.00
Thu 01/22 23Z 4.34 2530  84  29 -13 0.00
Fri 01/23 00Z 6.02 2530  87  30 -14 0.00
Fri 01/23 01Z 2.74 2530  83  32 -14 0.00
Fri 01/23 02Z 1.76 2529  83  28 -14 0.00
Fri 01/23 03Z 1.56 2529  80  28 -14 0.00
Fri 01/23 04Z 1.46 2532  81  26 -14 0.00
Fri 01/23 05Z 1.41 2532  83  25 -15 0.00
Fri 01/23 06Z 1.43 2533  82  25 -15 0.00
Fri 01/23 07Z 1.56 2531  84  27 -16 0.00
Fri 01/23 08Z 1.47 2530  87  23 -17 0.00
Fri 01/23 09Z 1.29 2627  87  25 -17 0.00
Fri 01/23 10Z 1.11 2526  85  28 -17 0.00
Fri 01/23 11Z 1.02 2427  86  28 -16 0.00
Fri 01/23 12Z 1.20 2432  87  38 -16 0.00
Fri 01/23 13Z 1.40 2432  88  31 -17 0.00
Fri 01/23 14Z 1.87 2430  89  34 -17 0.00
Fri 01/23 15Z 6.02 2426  90  26 -17 0.00
Fri 01/23 16Z 6.83 2523  90  22 -17 0.00
Fri 01/23 17Z 12.71 2624  81  26 -18 0.01
Fri 01/23 18Z 14.25 2624  72  31 -18 0.01
Fri 01/23 19Z 13.93 2622  71  43 -19 0.00
Fri 01/23 20Z 13.56 2624  72  59 -19 0.00
Fri 01/23 21Z 13.08 2626  69  66 -20 0.00
Fri 01/23 22Z 6.73 2628  68  68 -20 0.00
Fri 01/23 23Z 3.47 2729  75  69 -21 0.00
Sat 01/24 00Z 3.04 2826  84  69 -21 0.01
Sat 01/24 01Z 2.49 2926  83  63 -22 0.01
Sat 01/24 02Z 4.27 2925  81  55 -23 0.01
Sat 01/24 03Z 3.18 2924  80  40 -24 0.00
Sat 01/24 04Z 3.34 3025  83  31 -25 0.01
Sat 01/24 05Z 2.29 3028  77  23 -26 0.01
Sat 01/24 06Z 3.86 3030  69  23 -27 0.00
Sat 01/24 07Z 1.27 3032  57  26 -28 0.00
Sat 01/24 08Z 1.03 3032  64  27 -28 0.00
Sat 01/24 09Z 0.65 3032  68  26 -28 0.00
Sat 01/24 10Z 0.48 3132  67  22 -27 0.00
Sat 01/24 11Z 0.37 3131  64  18 -26 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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