NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260518_0000
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)
=== ===== === ==== ==== === === === ====
Mon 05/18 00Z 0.35 3212  65  20  11 0.00
Mon 05/18 01Z 0.26 3313  63  20  11 0.00
Mon 05/18 02Z 0.21 3312  62  23  11 0.00
Mon 05/18 03Z 0.18 3210  62  30  11 0.00
Mon 05/18 04Z 0.14 3207  62  31  11 0.00
Mon 05/18 05Z 0.15 2905  62  34  11 0.00
Mon 05/18 06Z 0.18 2706  62  38  12 0.00
Mon 05/18 07Z 0.19 2607  61  41  12 0.00
Mon 05/18 08Z 0.18 2407  63  50  13 0.00
Mon 05/18 09Z 0.19 2308  65  60  12 0.00
Mon 05/18 10Z 0.17 2110  69  64  12 0.00
Mon 05/18 11Z 0.18 2013  74  67  12 0.00
Mon 05/18 12Z 0.16 2016  80  74  12 0.00
Mon 05/18 13Z 0.15 1921  84  52  13 0.00
Mon 05/18 14Z 0.23 1926  87  49  13 0.00
Mon 05/18 15Z 0.37 2127  90  41  13 0.06
Mon 05/18 16Z 0.46 2225  87  27  13 0.02
Mon 05/18 17Z 0.56 2223  81  22  13 0.00
Mon 05/18 18Z 1.01 2222  82  29  13 0.00
Mon 05/18 19Z 2.87 2221  84  29  14 0.00
Mon 05/18 20Z 2.88 2221  84  23  14 0.00
Mon 05/18 21Z 2.62 2321  85  20  14 0.01
Mon 05/18 22Z 1.52 2321  85  22  14 0.01
Mon 05/18 23Z 1.18 2322  84  19  15 0.00
Tue 05/19 00Z 1.17 2423  86  20  15 0.01
Tue 05/19 01Z 1.14 2425  87  29  15 0.01
Tue 05/19 02Z 1.11 2427  83  25  15 0.00
Tue 05/19 03Z 0.92 2428  73  29  17 0.00
Tue 05/19 04Z 0.99 2530  68  15  17 0.00
Tue 05/19 05Z 1.05 2432  70  15  17 0.00
Tue 05/19 06Z 1.22 2436  79  44  16 0.00
Tue 05/19 07Z 1.22 2635  84  51  16 0.05
Tue 05/19 08Z 1.00 2633  76  51  16 0.03
Tue 05/19 09Z 1.11 2633  74  58  15 0.00
Tue 05/19 10Z 1.10 2730  73  56  15 0.00
Tue 05/19 11Z 1.01 2628  75  52  15 0.00
Tue 05/19 12Z 1.00 2627  79  41  14 0.00
Tue 05/19 13Z 0.89 2623  81  47  14 0.00
Tue 05/19 14Z 0.88 2522  81  64  15 0.00
Tue 05/19 15Z 1.03 2423  82  73  15 0.00
Tue 05/19 16Z 1.62 2423  86  62  15 0.00
Tue 05/19 17Z 3.23 2424  90  80  15 0.00
Tue 05/19 18Z 2.89 2424  91  84  15 0.01
Tue 05/19 19Z 3.61 2427  84  87  15 0.06
Tue 05/19 20Z 3.83 2525  84  79  15 0.00
Tue 05/19 21Z 2.47 2525  81  73  15 0.00
Tue 05/19 22Z 3.87 2526  84  62  15 0.00
Tue 05/19 23Z 1.79 2527  82  55  15 0.00
Wed 05/20 00Z 1.43 2429  86  56  15 0.00
Wed 05/20 01Z 1.01 2530  80  46  16 0.02
Wed 05/20 02Z 1.14 2534  78  49  16 0.00
Wed 05/20 03Z 1.40 2439  85  72  16 0.00
Wed 05/20 04Z 1.45 2441  88  73  16 0.00
Wed 05/20 05Z 1.34 2540  90  73  16 0.02
Wed 05/20 06Z 1.27 2539  90  78  15 0.03
Wed 05/20 07Z 1.22 2538  90  74  15 0.06
Wed 05/20 08Z 1.15 2535  91  54  15 0.02
Wed 05/20 09Z 1.24 2535  93  51  14 0.01
Wed 05/20 10Z 1.25 2635  96  61  13 0.02
Wed 05/20 11Z 1.29 2634  97  58  12 0.03

Run total areal avg QPF for the greens is: 0.48 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