NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260730_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)
=== ===== === ==== ==== === === === ====
Thu 07/30 00Z 0.65 1129  90  93  13 0.00
Thu 07/30 01Z 0.68 1130  91  92  13 0.03
Thu 07/30 02Z 0.67 1128  92  91  12 0.04
Thu 07/30 03Z 0.64 1226  92  91  12 0.01
Thu 07/30 04Z 0.60 1223  92  90  12 0.01
Thu 07/30 05Z 0.55 1120  91  89  12 0.01
Thu 07/30 06Z 0.50 1118  92  91  12 0.01
Thu 07/30 07Z 0.46 1016  91  91  12 0.01
Thu 07/30 08Z 0.41 0914  93  91  12 0.01
Thu 07/30 09Z 0.39 0813  93  91  12 0.01
Thu 07/30 10Z 0.39 0713  93  89  12 0.02
Thu 07/30 11Z 0.37 0612  91  88  12 0.02
Thu 07/30 12Z 0.24 0411  88  84  12 0.01
Thu 07/30 13Z 0.20 0212  84  80  12 0.00
Thu 07/30 14Z 0.21 0212  85  81  12 0.00
Thu 07/30 15Z 0.29 0213  86  83  11 0.00
Thu 07/30 16Z 0.33 0212  88  82  11 0.00
Thu 07/30 17Z 0.19 0110  86  78  12 0.00
Thu 07/30 18Z 0.12 0010  86  73  12 0.01
Thu 07/30 19Z 0.15 0109  83  64  13 0.05
Thu 07/30 20Z 0.12 3509  85  59  13 0.02
Thu 07/30 21Z 0.13 3411  87  58  13 0.00
Thu 07/30 22Z 0.07 3512  89  54  13 0.00
Thu 07/30 23Z 0.05 3514  91  57  13 0.01
Fri 07/31 00Z 0.05 0013  90  62  13 0.02
Fri 07/31 01Z 0.03 0014  89  66  13 0.01
Fri 07/31 02Z 0.03 0014  89  73  13 0.00
Fri 07/31 03Z 0.05 0014  89  78  13 0.00
Fri 07/31 04Z 0.04 0012  89  77  13 0.00
Fri 07/31 05Z 0.07 3512  89  79  13 0.00
Fri 07/31 06Z 0.06 3512  87  78  13 0.00
Fri 07/31 07Z 0.07 3412  85  78  13 0.00
Fri 07/31 08Z 0.07 3412  82  74  13 0.00
Fri 07/31 09Z 0.03 3511  80  69  13 0.00
Fri 07/31 10Z 0.07 3412  80  68  12 0.00
Fri 07/31 11Z 0.08 3412  81  68  12 0.00
Fri 07/31 12Z 0.11 3412  86  61  12 0.00
Fri 07/31 13Z 0.11 3411  90  58  12 0.00
Fri 07/31 14Z 0.10 3410  91  54  12 0.00
Fri 07/31 15Z 0.17 3310  93  54  12 0.01
Fri 07/31 16Z 0.23 3311  91  58  11 0.01
Fri 07/31 17Z 0.35 3312  89  55  12 0.00
Fri 07/31 18Z 0.67 3210  87  44  12 0.00
Fri 07/31 19Z 0.83 3109  87  33  12 0.00
Fri 07/31 20Z 0.71 3109  87  38  13 0.00
Fri 07/31 21Z 0.53 3109  86  43  13 0.01
Fri 07/31 22Z 0.37 3008  89  50  13 0.01
Fri 07/31 23Z 0.28 3108  87  54  13 0.02
Sat 08/01 00Z 0.27 3109  85  50  13 0.01
Sat 08/01 01Z 0.24 3108  83  40  13 0.00
Sat 08/01 02Z 0.23 3107  83  36  13 0.01
Sat 08/01 03Z 0.28 3007  86  27  13 0.00
Sat 08/01 04Z 0.28 2906  87  24  13 0.00
Sat 08/01 05Z 0.23 2906  84  20  13 0.00
Sat 08/01 06Z 0.20 2805  82  18  13 0.00
Sat 08/01 07Z 0.17 2704  79  22  13 0.00
Sat 08/01 08Z 0.17 2504  78  19  13 0.00
Sat 08/01 09Z 0.18 2404  78  20  13 0.00
Sat 08/01 10Z 0.19 2305  78  23  13 0.00
Sat 08/01 11Z 0.22 2306  79  25  13 0.00

Run total areal avg QPF for the greens is: 0.39 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