NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260704_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)
=== ===== === ==== ==== === === === ====
Sat 07/04 06Z 0.56 2919  79  78  17 0.00
Sat 07/04 07Z 0.64 2923  80  64  17 0.00
Sat 07/04 08Z 0.63 3023  82  64  16 0.00
Sat 07/04 09Z 0.57 3022  84  62  16 0.00
Sat 07/04 10Z 0.48 3121  85  59  16 0.00
Sat 07/04 11Z 0.38 3119  83  52  16 0.00
Sat 07/04 12Z 0.36 3117  81  55  16 0.00
Sat 07/04 13Z 0.37 3015  83  59  16 0.00
Sat 07/04 14Z 0.43 2915  85  69  16 0.00
Sat 07/04 15Z 0.53 2916  87  79  15 0.00
Sat 07/04 16Z 0.64 2916  92  84  15 0.00
Sat 07/04 17Z 0.55 2914  94  76  15 0.10
Sat 07/04 18Z 0.60 3115  90  72  15 0.02
Sat 07/04 19Z 0.61 3114  87  60  15 0.00
Sat 07/04 20Z 1.35 3214  84  58  15 0.00
Sat 07/04 21Z 1.51 3214  83  47  14 0.07
Sat 07/04 22Z 1.00 3213  82  39  14 0.00
Sat 07/04 23Z 0.40 3314  79  34  14 0.00
Sun 07/05 00Z 0.22 3315  75  30  14 0.00
Sun 07/05 01Z 0.08 3415  74  25  13 0.00
Sun 07/05 02Z 0.04 3413  72  28  13 0.00
Sun 07/05 03Z 0.06 3514  70  23  13 0.00
Sun 07/05 04Z 0.11 3513  69  15  13 0.00
Sun 07/05 05Z 0.11 0011  69  20  13 0.00
Sun 07/05 06Z 0.13 0010  69  24  13 0.00
Sun 07/05 07Z 0.20 0209  70  18  12 0.00
Sun 07/05 08Z 0.19 0208  70  16  12 0.00
Sun 07/05 09Z 0.16 0207  72  20  12 0.00
Sun 07/05 10Z 0.19 0307  73  13  12 0.00
Sun 07/05 11Z 0.21 0307  72  12  11 0.00
Sun 07/05 12Z 0.21 0306  72   8  11 0.00
Sun 07/05 13Z 0.27 0305  74   7  11 0.00
Sun 07/05 14Z 0.69 0403  76   7  11 0.00
Sun 07/05 15Z 0.83 0401  78   8  11 0.00
Sun 07/05 16Z 0.55 0301  80   8  11 0.00
Sun 07/05 17Z 0.21 0001  80  14  12 0.01
Sun 07/05 18Z 0.17 3301  81  12  12 0.00
Sun 07/05 19Z 0.17 3402  81   9  12 0.00
Sun 07/05 20Z 0.18 3503  81   7  12 0.00
Sun 07/05 21Z 0.16 3503  82   9  12 0.00
Sun 07/05 22Z 0.25 0104  81   8  12 0.01
Sun 07/05 23Z 0.28 0304  80   7  12 0.00
Mon 07/06 00Z 0.36 0404  80   4  12 0.00
Mon 07/06 01Z 0.47 0606  79   4  12 0.00
Mon 07/06 02Z 0.53 0707  78   4  12 0.00
Mon 07/06 03Z 0.52 0807  79   4  11 0.00
Mon 07/06 04Z 0.58 0908  80   3  11 0.00
Mon 07/06 05Z 0.49 1008  79   3  11 0.00
Mon 07/06 06Z 0.37 1208  81   4  11 0.00
Mon 07/06 07Z 0.26 1309  83   4  11 0.00
Mon 07/06 08Z 0.17 1410  84   4  11 0.00
Mon 07/06 09Z 0.14 1511  85   4  11 0.00
Mon 07/06 10Z 0.10 1512  87   4  11 0.00
Mon 07/06 11Z 0.12 1512  87   3  11 0.00
Mon 07/06 12Z 0.12 1511  83   3  11 0.00
Mon 07/06 13Z 0.13 1510  82   3  11 0.00
Mon 07/06 14Z 0.17 1409  80   3  10 0.00
Mon 07/06 15Z 0.43 1409  80   3  10 0.00
Mon 07/06 16Z 0.96 1308  81   3  11 0.00
Mon 07/06 17Z 1.64 1308  82   3  11 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