Schaefer Chiropractic Center, Ltd., et al., Appellants, vs. Farmers & Merchants State Bank, Respondent, Patricia Vogt, Respondent.

may not be cited except as provided by

Minn. Stat. § 480 A. 08, subd. 3 (1996).

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 C6-97-1159

State of Minnesota,

Respondent,

vs.

Ricky Joseph Farmer,

Appellant.

 Filed March 17, 1998

 Affirmed

 Peterson, Judge

Mille Lacs County District Court

File No. K296502

Hubert H. Humphrey III, Attorney General, Nancy J. Bode, Assistant Attorney General, 1400 NCL Tower, 445 Minnesota Street, St. Paul, MN 55101; and

Jennifer Fahey, Mille Lacs County Attorney, Mille Lacs County Courthouse, 635 Second Street Southeast, Milaca, MN 56353 (for respondent)

Mark D. Kelly, 115 First Street Southwest, P.O. Box 163, Milaca, MN 56353 (for appellant)

Considered and decided by Crippen, Presiding Judge, Lansing, Judge, and Peterson, Judge.

 U N P U B L I S H E D O P I N I O N

 PETERSON, Judge

In this appeal from a conviction for gross misdemeanor driving under the influence of alcohol (DWI), appellant argues that the district court erred in denying his motion to suppress the results of a breath test. We affirm.

 FACTS

At about 10:30 p.m., Mille Lacs Tribal Police Officer Gar Pemberton was contacted about a report from the Minnesota State Patrol regarding a vehicle traveling northbound in the southbound lane of Highway 169. About a half-hour later, Pemberton stopped at Grand Casino and spoke to two witnesses who had reported the vehicle traveling in the wrong lane. One of the witnesses identified the vehicle as a white Eagle Premier with a Montana license plate. The vehicle was parked in the casino valet parking lot, but casino personnel were unable to identify the driver. Pemberton asked casino personnel to contact him if the driver claimed the vehicle.

At about 1:00 a.m., Pemberton was informed that the vehicle was about to leave the casino. Pemberton drove to the casino and saw the vehicle leave, turning south onto Highway 169. Pemberton followed the vehicle and saw it cross the centerline and the fog line several times. Pemberton also testified that the vehicle repeatedly speeded up and slowed down between 40 and 60 miles per hour.

Pemberton stopped the vehicle and spoke to the driver, appellant Ricky Joseph Farmer. Pemberton testified that he detected a strong odor of an alcoholic beverage, and that Farmer's eyes were bloodshot, watery, and glassy. Pemberton asked Farmer to perform a finger-to-nose field sobriety test, but cerebral palsy prevented Farmer from properly performing the test. Pemberton had Farmer perform the horizontal gaze nystagmus test but did not testify as to the result. Pemberton did not ask Farmer to perform any other field sobriety tests and did not offer Farmer a preliminary breath test.

Pemberton arrested Farmer and transported him to jail. An officer read Farmer the implied consent advisory, and Farmer agreed to submit to a breath test. The test results showed an alcohol concentration of .11.

Farmer was charged by complaint with three counts of gross misdemeanor DWI and one count of driving after suspension. Farmer moved to suppress the breath test results on the ground that the arresting officer lacked probable cause to believe Farmer was under the influence of alcohol and, therefore, was not authorized to administer the breath test. The district court denied Farmer's motion. Pursuant to State v. Lothenbach, 296 N.W.2d 854, 857 (Minn. 1980), Farmer entered a conditional guilty plea to one count of gross misdemeanor DWI, preserving his right to appeal the denial of his motion to suppress the breath test results. This appeal is from the guilty plea.

 D E C I S I O N

Minn. Stat. § 169.121, subd. 1(a), (d) (1994), makes it a crime for a person to drive a motor vehicle when the person is under the influence of alcohol or when the person has an alcohol concentration of .10 or greater. A chemical test of a person's breath to determine the presence of alcohol may be required of a person when an officer has probable cause to believe the person was driving a motor vehicle in violation of section 169.121, and the person has been lawfully arrested for violating section 169.121. Minn. Stat. § 169.123, subd. 2(a)(1) (1994).

An officer can lawfully arrest a person for DWI when the officer has probable cause to believe the person was driving a motor vehicle while under the influence of alcohol. State v. Olson, 342 N.W.2d 638, 640-41 (Minn. App. 1984). Probable cause to believe a person was driving under the influence

exists when facts and circumstances are known to the officer that would warrant a prudent person in the officer's position to conclude the person was violating the DWI statute.

 Holm v. Commissioner of Pub. Safety, 416 N.W.2d 473, 475 (Minn. App. 1987) (citing State v. Harris, 295 Minn. 38, 42, 202 N.W.2d 878, 881 (1972)).

In evaluating probable cause, "each case must be decided on its own facts," and a reviewing court should accord "an officer's probable cause determination 'great deference.'" Id. (quoting Olson, 342 N.W.2d at 640-41).

The reviewing court must ensure that the officer had a substantial basis for concluding that probable cause existed at the time the implied consent law was invoked.

 Id. (citing Olson, 342 N.W.2d at 641).

Farmer argues that the state failed to present sufficient evidence to support the district court's finding that Pemberton had probable cause to believe Farmer was under the influence of alcohol. Farmer cites the absence of evidence that he failed any field sobriety tests. But field sobriety tests are not required to support an officer's probable cause determination that a driver is intoxicated. Holtz v. Commissioner of Pub. Safety, 340 N.W.2d 363, 365 (Minn. App. 1983). Farmer also cites Pemberton's failure to offer him a preliminary breath test. But a preliminary screening test is not required before administering a chemical test under the implied consent statute when "the officer ascertains from his own observations that the driver is under the influence of alcohol." Marben v. State, Dep't of Pub. Safety, 294 N.W.2d 697, 700 (Minn. 1980).

Pemberton observed Farmer's vehicle cross the centerline and the fog line several times, and repeatedly speed up and slow down between 40 and 60 miles per hour. Upon stopping the vehicle, he detected a strong odor of an alcoholic beverage, and observed that Farmer's eyes were bloodshot, watery, and glassy. This evidence supports the district court's finding that Pemberton had probable cause to believe Farmer was under the influence of alcohol. See State v. Aschnewitz, 483 N.W.2d 107, 109 (Minn. App. 1992) ("officer had probable cause to believe that appellant had committed the offense of driving under the influence when he saw appellant's vehicle swerve off of the road and smelled alcohol on appellant's breath"); Keane v. Commissioner of Pub. Safety, 360 N.W.2d 357, 359-60 (Minn. App. 1984) (officer's observation of moderate odor of alcohol, balance problem, and very erratic driving sufficient to establish probable cause). The district court did not err in denying Farmer's motion to suppress the breath test results.

  Affirmed.