NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260712_1200
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)
=== ===== === ==== ==== === === === ====
Sun 07/12 12Z 0.25 0105  76  18  10 0.00
Sun 07/12 13Z 0.25 0105  77  15  10 0.00
Sun 07/12 14Z 0.45 0004  79  13  10 0.00
Sun 07/12 15Z 0.65 0003  81  11  10 0.00
Sun 07/12 16Z 0.50 0003  81  10  10 0.00
Sun 07/12 17Z 0.49 3401  81  10  11 0.00
Sun 07/12 18Z 0.55 3102  81  11  11 0.00
Sun 07/12 19Z 0.68 2903  80  16  11 0.00
Sun 07/12 20Z 0.76 2903  76  16  12 0.00
Sun 07/12 21Z 0.76 3003  72  15  12 0.00
Sun 07/12 22Z 0.39 2903  68  20  12 0.00
Sun 07/12 23Z 0.15 2902  66  27  12 0.00
Mon 07/13 00Z 0.17 2302  65  15  12 0.00
Mon 07/13 01Z 0.24 2304  64  12  12 0.00
Mon 07/13 02Z 0.32 2305  65  18  12 0.00
Mon 07/13 03Z 0.46 2307  69  12  12 0.00
Mon 07/13 04Z 0.59 2309  73  14  12 0.00
Mon 07/13 05Z 0.77 2412  76  14  11 0.00
Mon 07/13 06Z 0.87 2414  79  20  11 0.00
Mon 07/13 07Z 0.87 2515  80  21  11 0.00
Mon 07/13 08Z 0.89 2616  77  23  11 0.00
Mon 07/13 09Z 0.89 2716  74  28  11 0.00
Mon 07/13 10Z 0.77 2615  71  30  12 0.00
Mon 07/13 11Z 0.67 2614  70  40  12 0.00
Mon 07/13 12Z 0.56 2613  67  50  12 0.00
Mon 07/13 13Z 0.49 2512  66  63  13 0.00
Mon 07/13 14Z 0.47 2511  64  73  13 0.00
Mon 07/13 15Z 0.52 2412  62  83  13 0.00
Mon 07/13 16Z 0.71 2412  61  87  13 0.00
Mon 07/13 17Z 1.20 2412  60  88  14 0.00
Mon 07/13 18Z 1.35 2412  58  87  14 0.00
Mon 07/13 19Z 1.11 2312  61  85  15 0.00
Mon 07/13 20Z 1.00 2314  67  82  15 0.00
Mon 07/13 21Z 1.00 2417  72  85  15 0.00
Mon 07/13 22Z 0.88 2419  77  87  15 0.00
Mon 07/13 23Z 0.79 2520  80  84  15 0.01
Tue 07/14 00Z 0.86 2523  81  78  15 0.01
Tue 07/14 01Z 0.99 2624  79  69  15 0.00
Tue 07/14 02Z 1.05 2624  76  59  15 0.00
Tue 07/14 03Z 0.98 2725  70  52  16 0.00
Tue 07/14 04Z 0.94 2725  69  43  15 0.00
Tue 07/14 05Z 0.79 2825  77  42  16 0.00
Tue 07/14 06Z 0.72 2824  83  32  16 0.01
Tue 07/14 07Z 0.70 2824  83  24  16 0.01
Tue 07/14 08Z 0.64 2824  87  20  16 0.01
Tue 07/14 09Z 0.63 2825  88  23  17 0.01
Tue 07/14 10Z 0.62 2826  87  27  17 0.01
Tue 07/14 11Z 0.64 2827  84  37  18 0.01
Tue 07/14 12Z 0.68 2729  83  38  19 0.00
Tue 07/14 13Z 0.71 2730  78  36  19 0.00
Tue 07/14 14Z 0.74 2729  78  33  19 0.00
Tue 07/14 15Z 0.80 2729  82  27  19 0.00
Tue 07/14 16Z 0.83 2728  83  23  19 0.00
Tue 07/14 17Z 0.92 2627  86  18  19 0.00
Tue 07/14 18Z 1.28 2627  87  15  19 0.00
Tue 07/14 19Z 2.58 2626  85  19  19 0.00
Tue 07/14 20Z 2.47 2626  85  22  19 0.00
Tue 07/14 21Z 2.28 2627  84  24  20 0.00
Tue 07/14 22Z 1.56 2628  85  27  20 0.00
Tue 07/14 23Z 1.48 2630  88  34  20 0.00

Run total areal avg QPF for the greens is: 0.08 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