NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260205_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 02/05 00Z 0.36 3115  79  31 -12 0.00
Thu 02/05 01Z 0.29 3117  80  30 -12 0.00
Thu 02/05 02Z 0.30 3117  84  33 -12 0.00
Thu 02/05 03Z 0.30 3015  85  33 -12 0.00
Thu 02/05 04Z 0.26 3014  83  35 -12 0.00
Thu 02/05 05Z 0.29 2915  83  38 -12 0.00
Thu 02/05 06Z 0.31 2916  85  37 -12 0.00
Thu 02/05 07Z 0.32 2916  85  36 -12 0.00
Thu 02/05 08Z 0.35 2917  84  37 -13 0.00
Thu 02/05 09Z 0.39 2918  84  45 -13 0.00
Thu 02/05 10Z 0.38 2918  84  59 -13 0.00
Thu 02/05 11Z 0.36 3019  85  76 -14 0.00
Thu 02/05 12Z 0.35 3018  86  63 -15 0.00
Thu 02/05 13Z 0.33 3018  85  12 -15 0.00
Thu 02/05 14Z 0.28 3118  81   1 -15 0.00
Thu 02/05 15Z 0.25 3117  79   2 -15 0.00
Thu 02/05 16Z 0.23 3116  77   2 -15 0.00
Thu 02/05 17Z 0.21 3114  74   3 -15 0.00
Thu 02/05 18Z 0.20 3113  71   4 -15 0.00
Thu 02/05 19Z 0.19 3212  66   3 -15 0.00
Thu 02/05 20Z 0.15 3212  60   3 -14 0.00
Thu 02/05 21Z 0.13 3212  57   3 -13 0.00
Thu 02/05 22Z 0.12 3212  57   3 -13 0.00
Thu 02/05 23Z 0.10 3212  54   4 -12 0.00
Fri 02/06 00Z 0.07 3310  52   4 -12 0.00
Fri 02/06 01Z 0.07 3310  52   5 -12 0.00
Fri 02/06 02Z 0.04 3309  48   5 -11 0.00
Fri 02/06 03Z 0.01 3408  43   6 -11 0.00
Fri 02/06 04Z 0.01 3505  38   8 -10 0.00
Fri 02/06 05Z 0.01 3503  35   9 -10 0.00
Fri 02/06 06Z 0.01 3501  33   9 -10 0.00
Fri 02/06 07Z 0.01 3500  32   7 -10 0.00
Fri 02/06 08Z 0.01 2400  31   6 -10 0.00
Fri 02/06 09Z 0.02 2001  30   6 -10 0.00
Fri 02/06 10Z 0.03 1903  30   6 -10 0.00
Fri 02/06 11Z 0.03 1903  30   7 -10 0.00
Fri 02/06 12Z 0.05 2103  29   8 -10 0.00
Fri 02/06 13Z 0.05 2203  29  15 -10 0.00
Fri 02/06 14Z 0.04 2103  32  41 -10 0.00
Fri 02/06 15Z 0.05 2004  37  63 -11 0.00
Fri 02/06 16Z 0.08 2104  41  81 -11 0.00
Fri 02/06 17Z 0.09 2204  44  86 -11 0.00
Fri 02/06 18Z 0.09 2104  48  86 -11 0.00
Fri 02/06 19Z 0.09 2104  53  87 -11 0.00
Fri 02/06 20Z 0.14 2204  54  87 -12 0.00
Fri 02/06 21Z 0.17 2205  56  88 -12 0.00
Fri 02/06 22Z 0.17 2206  55  88 -12 0.00
Fri 02/06 23Z 0.18 2207  48  89 -11 0.00
Sat 02/07 00Z 0.20 2207  48  89 -11 0.00
Sat 02/07 01Z 0.21 2308  53  88 -11 0.00
Sat 02/07 02Z 0.26 2309  63  88 -12 0.00
Sat 02/07 03Z 0.26 2309  79  89 -12 0.00
Sat 02/07 04Z 0.21 2307  88  89 -12 0.00
Sat 02/07 05Z 0.17 2306  90  88 -12 0.01
Sat 02/07 06Z 0.17 2405  91  87 -12 0.01
Sat 02/07 07Z 0.18 2505  91  86 -12 0.01
Sat 02/07 08Z 0.16 2805  91  87 -12 0.01
Sat 02/07 09Z 0.13 3106  91  85 -13 0.01
Sat 02/07 10Z 0.11 3309  90  83 -13 0.01
Sat 02/07 11Z 0.08 3415  90  82 -14 0.02

Run total areal avg QPF for the Central_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